I have a Auzentech X-plosion Cinema 7.1 which also has a C-Media chip. The "current" available drivers for it performed badly (BSOD's)
until build 7000, when they miraculously started working problem free.
My cards drivers are multi-verse drivers (x32/x64/XP/Vista) which actually use the XP interface instead of the Vista interface on Seven.
Perhaps try installing the Vista drivers with XP compatibility mode. Or even try the XP drivers instead.
What cards are these exactly? on-board/PCI/PCI-e etc? Maybe try to grab the drivers from the manufacturers and not directly from C-Media.
I contacted Auzentech support several months ago and they claimed that C-Media were releasing Seven beta drivers around June. However that was several months ago and a lot of things could have changed....