That is easy. touchpads selection but 7.1 playback thru another amp is tricky - done in my home automation system.
How did you manage 7.1 output? Was it via HDMI?
If it is HDMI, which hardware (sound or video card) did you use?
I have Dell Laptop (I5 and Intel onboard audio) and AMD on board chipset based desktop. With Linux, I can only get Stereo out of HDMI. If HDMI is working for you, I can port driver code to the hardware that I have.
-Shamit