UPDATE: this is out of date and although it worked for me at the time, there is a better solution to make it work: https://github.com/evilphish/sennheiser-gsx-1000
In order to make the Sennheiser amplifier GSX 1000/1200 work on Linux as a 7.1 device it is needed to change a configuration file of pulseaudio. Execute this command to identify the output sound cards:
aplay -l
This is a sample output
card 1: Audio [GSX 1000 Main Audio], device 0: USB Audio [USB Audio]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 1: Audio [GSX 1000 Main Audio], device 1: USB Audio [USB Audio #1]
Subdevices: 0/1
Subdevice #0: subdevice #0
To identify the input sound cards:
arecord -l
This is a sample outuput
card 1: Audio [GSX 1000 Main Audio], device 0: USB Audio [USB Audio]
Subdevices: 0/1
Subdevice #0: subdevice #0
For the playback, subdevice 1/1 is the 7.1 playback device ("Speakers" equivalent on Windows) and the subdevice 0/1 should be the "Headset earphone". Edit /etc/pulse/default.pa, uncomment the lines below and set the correct device:
load-module module-alsa-source device=hw:1,0 # capture device, card 1, subdevice 0
load-module module-alsa-sink device=hw:1,1 channels=8 # playback device, card 1, subdevice 1, 7.1 channels
Information taken from here
Greetings guys, I created a udev / pulseaudio device config version of this and in addition I also got the seperate output for the chat function working. You can basically patch mumble into the second output and control the offset volume in regard to the base volume with the small knob on the right. That version should also be invariant towards sound card changes in your system. Feel free to check it out https://github.com/evilphish/sennheiser-gsx-1000.