The GSP 601 headset has the same beefy plastic frame construction and metal articulating hinge design as the GSP 670 wireless headset, which is so similar you could easily mistake the two. The GSP 601 headset also has interchangeable side fascias, as well as detachable earpads, which have the characteristic human ear shape; hence the earpads are wider at the top (4cm wide) and narrower towards the bottom (2.5cm wide). The height dimensions of the ear pads are 7cm (inner) and 11cm (outer), while the outer width is 7cm wide (top) and 5cm (bottom).
Different color side fascias are also included, which give the GSP 670 headset a subtle change. Removing the side fascias is straightforward via the small slit at the bottom, although it may require prying open with a pointy plastic tool if your fingernails are not hard enough. Each side fascia weighs 6 grams.
The EPOS Sennheiser GSP 601 articulating hinge has an aerated design and two metal bolts securing the hinge in two places. The GSP 601 hinge has an outstanding nifty construction, doubling as the mechanism for tilting and swiveling the earcups. That said, the articulating hinge does have limited range of motion with just a few degrees of movement; hence you cannot fully swivel the earcups flush against a surface.
While the GSP 601 could visually pass as the GSP 670 twin, the similarities end there since the GSP 601 is exclusively a wired headset. The GSP 670 does have the convenience of dual wireless mode (2.4Ghz and Bluetooth) but, the GSP 601 has the reliability and performance of a wired connection, which makes all the difference when gaming and listening to music.
Being a wired headset, the Sennheiser GSP 601 uses an auxiliary input to connect to any audio device that accepts a 3.5mm audio connection. This includes Xbox One controllers, Playstation 4 controllers, Windows computers and Mac computers. The Sennheiser GSP 601 comes with two sets of audio cables, both of which have a soft braided sheath and hard plastic plug connectors which are reinforced with thick rubber strain reliefs.
The included cables are Sennheiser branded, namely the GSA 505 PC cable (2.5 meter long) and the GSA 506 console cable, which is a 1.2 meter long cable with a 3.5mm connector and right angle rubber plug. Both audio cables are not run-of-the-mill, not only because they are good quality but also because of their RCA connector like design. Both cables have a recessed 2.5mm mini connector that connects into the left earcup of the GSP 601 headset. The GSA 505 PC cable weighs 35 grams, while the GSA 506 console cable weighs 19 grams.
The 2.5mm connector is literary built inside the plug and will only fit the GSP 601 headset via the left earcup; hence the GSP 601 has a single sided entry headphone cable. While you won't be able to use a regular audio cable with the GSP 601, the included cables do have the advantage of offering a more secure connection and less chance of the connector breaking off because three-quarters of the plug inserts all the way into the audio port on the headset, which is also recessed.
Neither the GSA 505 and GSA 506 cables can transmit surround sound. In fact, the GSP 601 headset is not equipped with a 7.1 sound adapter, which is needed in order to get 7.1 surround sound. If you do want surround sound, you will need an adapter like the GSX 1000 audio amp or, you can emulate surround sound using "Windows Sonic for headphones", which is a software feature built-in to Xbox One and Windows 10 computers. The GSP 670 model and GSP 370 model do have 7.1 sound built-in, as well as two separate in-chat and audio volume wheels (the GSP 601 doesn't).
The EPOS Sennheiser GSP 601 headset comes in only one color variant and that is white with copper accents, which can be seen throughout the headphone, including the boom arm microphone, which is made of a chunky hard plastic, measuring 2cm wide. There is a rubber trim in the mid-section that gives the boom arm flexibility, although it does not allow the mic to bend into place since there is no memory wire built-in. The boom arm mic is non-detachable but, it does have a wide range of motion, allowing you to positioning it upright 90 degrees and and all the way down beneath the chin.
As far as microphone quality, the GSP 601 microphone sounds very good and on par with the GSP 300 wired headset, although the GSP 601 bi-directional microphone provides fuller sound and better dynamic range than the GSP 300 uni-directional mic. There is no mic monitoring/sidetone feature on any of these headsets; hence you cannot hear yourself talk. Compared to the GSP 670, the GSP 601 mic is better, which is not surprising since wireless headphones generally can't compete with wired ones when it comes to microphone quality.
There is no hardshell carry case included for transporting the GSP 601 headset but, you can use the packaging box the headset came with. The box has a hard outer shell with thick closed-cell foam padding on both sides, which does a good job of protecting the headset. The foam is glued to the inside of the box. Another use you can get out of the packaging box is as a headset stand by sitting up the bottom half of the box. The foam cutout is deep, which allows the headphones to rest securely against the foam while the box sits upright.
The GSP 601 headband also has a plastic construction with a 5.8cm wide aerated frame and split foam padding design (1cm thick), which help minimize hot spot on top of the head. The adjusting band of the headland is also made of plastic and can be easily slid up and down while wearing the headset. The headband tensioning system works just like in the GSP 670 via two sliders, which slightly lower the clamping force. The GSP 601 headset has naturally a high clamping force by default, which is how it's able to achieve superb passive noise isolation.
The GSP 601 weighs 400 grams (without cables), which is exactly the same weight as the GSP 670; hence in the heavy weight category. Whether the weight will be an issue for you or not will depend on whether you're used to wearing weighty headphones and also the fit. The GSP 601 should fit comfortably though, thanks to the earcup adjustment.
The GSP 601 earcups have a proper over-ear design with large hole ear pad openings with 3cm depth, which should envelop most ear sizes. The earpads have 2.5cm thick memory foam padding that cushions the clamping force and weight of the headset. This creates a good isolating seal and good ventilation too, thanks to the earpads being detachable, which allows air to naturally flow through the slit opening to lower heat/sweat build up.
The earpads are covered with three different materials. Breathable close-knit mesh (inside lining), leatherette (outside perimeter) and suedette (front of the earpads).The earpads are Sennheiser branded - model GSA 601 - and go a good job of blocking out surrounding noise and prevent a lot of sound leakage at max volume. On the back of the GSP 601 earcups there is a large vent port to enhance the bass response.
The GSP 601 volume knob uses a potentiometer with two stops for max volume and minimum volume and, it has a strong resistance, which provides a more gradual volume adjustment. The other type of volume wheel used on some gaming headsets uses a rotary encoder, which makes the volume wheel have an infinite scroll similar to the scroll wheel of a mouse. 
A volume potentiometer seems more natural for volume control though. The GSP 601 volume wheel can crank up a good amount of volume without distortion, although the volume is preset, meaning you cannot further increase the volume from the source system volume since it's limited by the headset.
The GSP 601 volume knob has notches, which adds grip preventing the fingers from slipping off. The GSP 601 volume wheel doesn't make a soft click when the volume is muted like the GSP 500 headset does. The GSP 601 boom arm microphone does make an audible soft click to indicate microphone sound is muted. The mic mute switch is positioned midway so, rotating the boom arm past 45 degrees will activate the mute; hence you don't have to flip the boom arm all the way to the 90-degree position. The boom arm measures 14cm long.

The GSP 601 earcups house 50mm drivers (28 Ohm resistance), which are protected by a layer of lycra material to minimize dirt ingress. The GSP 601 earpads have the same detachable mechanism as the GSP 670, using plastic retainers to snap the earpads on and off. The earpads weigh 23 grams each.
While the GSP 601 don't have virtual surround, the stereo drivers deliver wide soundstage with a lot a bass to feel fully immersed. The bass is punchy but does not overwhelm the overall soundstage; hence you can still appreciate instrument, vocals and in-game footsteps, thanks to clear midrange and crisp treble. The old saying "if it ain't broke, don't fix it" really comes to mind when looking at the GSP 601, which EPOS has kept true to its roots with virtually the same headset design, going back as far as the GSP 350 that was released 4 years ago. You can buy the EPOS Sennheiser GSP 601 headset from EPOS at a great price right now down from £199 to £129.