I have been using the GSX1000 with the Game Zero headphones for about a year playing CSGO and Quake Champions exclusively, so I have a strong sense of what the audio sounds like in these games.
I just upgraded to the GSP 600 headphones a few weeks ago and I must say these changed my impression of the GSX 1000 quite substantially.
I tested the GSX 1000 + GSP 600/Game Zeros on 2.0 HD Stereo with Stereo Headphones/Speakers and CS GO 3D in game processing, compared this to the 7.1 surround + 5.1 in game surround options and I can attest the GSX 1000 sounds better on both headsets. The up/down position qualities on the CS GO in engine solution are better, but you can frequently hear small artifacting in the effects when A/B testing it against the GSX 1000. The GSX 1000 has way clearer directional information and you can better tell depth/distance of sounds, however the up/down positional information is noticeably worse than in game 3D positional audio over stereo, but that should be expected if you understand how these solutions work.
The best setting for the GSX 1000 positional audio is 7.1 mode in Windows, 5.1/7.1 Speaker mode in the game (if available), nothing set additionally on the GSX 1000. I have seen a few people suggest thing setting, it's the best option, so if this setting sounds bad on your headphones, buy different headphones for a different sound signature.
The Game Zero headphones are 150Ohm, which is probably the maximum the GSX 1000 is capable of properly supporting, but the sound is not as punchy as from a more powerful source (I have tested this on a Mayflower and Sound Blaster X). The Game Zero was not a bass oriented headphone, and due to the limited power available I was never very impressed with the setup on the GSX 1000. I would use the Music EQ, 7.1, Front Speaker Boost and that sounded quite good all round in music and games, but all the effects seemed to impair the positional nature of the sound, despite making it less harsh and more full with a better low end.
The GSP 600 on the other hand has heaps of bass, I would argue too much to even bother using any of the EQs on the GSX 1000, but that's a good thing as you want that 7.1 clean settings configuration on the device. The headphone is 50Ohm, which is way more suitable for the GSX 1000 power situation and the power and bass is very strong in 7.1 with very clear position qualities and as much or better clarity than the Game Zero. Much of this is probably also due to the physical design of the GSP 600 clamping the cups significantly better, though the headset looks like some sort of device or a hat rather than a headphone, whatevs.
It is still however, hopeless for music in 7.1 configuration. The only configuration that is suitable whatsoever for music listening, is the 2.0 HD mode on the GSX 1000. It does sound exceptional on the GSP 600, much better than the same setting on the Game Zero and that's due to the power delivery IMO. The only issue with this is it's not a setting on the device, rather you need to configure it manually to stereo and then the higher resolution output. Very annoying when you want 7.1 settings for CSGO and then back to 2.0 HD for music, then back to 7.1 for a show or a movie. This is by far the worst part of the design and perhaps could be resolved with firmware, though I expect not without a desktop client, which I am not opposed to if for that sole purpose btw. Did I mention it is super annoying! mostly because both modes are so good, but for totally different purposes and using the 7.1 setting on music is OK, but so dramatically better on the 2.0 HD configuration it's annoying not use it. For clarity the 2.0 setting on the amp while in 16 bit mode sounds worse than the 2.0 HD 24 bit mode, I doubt due to resolution alone, but it sounds obviously worse so it's really not useful.
I feel as though the GSP 600 is a solid product on it's own and capable of sounding good on high quality motherboard audio or better and you can rely on in game surround features that are common in many games now days. The Game Zero is an odd product, they are really tuned for an open sound on their own so are better with 2.0 input IMO, but require more power and an EQ tweak to sound good and the GSX 1000 simply doesn't offer that. The GSX 1000 is also a product that is quite expensive for what you get, fairly limited in terms of functionality and a low power output, though it it seems to work perfectly with the GSP 600. I assume this is very obviously the point, to buy both and that is what I would suggest.
I think I would strongly recommend the GSP500 or GSP600 alongside the GSX 1000, over most other configurations I can think of in a similar total price range for gaming audio, it does the best 7.1 effect I have heard and I have tested most hardware options available. I would suggest the Game Zero with a high end Sound Blaster or Xonar card with a bit of power and an EQ probably in 2.0 mode. But individually I probably wouldn't recommend any of these products, other than the GSP 600, but its expensive.
like undecipherable surround mess. I thought my ears were broken for a bit till i realised my mistake 
