I'm currently using the GSX1000 myself. Make sure on your PC you right click on the sound devices (the speaker icon on the taskbar, select sound devices, then right click on the GSX main audio. Configure speakers to 7 channels, and save all that. On the GSX itself, make sure to select 7.1, on the wavy line on the gsx display and make sure it shows one white plus symbol, for a standard room size (for best surround balance). I suggest leaving everything else off on the gsx dsiplay. The only white icons should be the plus button on the wavy line on the left, the headphone icon on the top left, and the 7.1 on the bottom right.
And for games itself, NEVER PICK THE HEADPHONE OPTION IN GAME. That is made for basic signals. These devices are MEANT to be set to home theater, speaker type presets because THEN the device mixes it down for your headphone. Again. DO NOT PICK THE HEADPHONE OPTIONS IN GAME WHEN USING VIRTUAL SURROUND DEVICES LIKE THE GSX 1000.
If that does not help you, then I dunno. You're screwed. I don't have CSGO and don't know the in game options.