After a few days trying some different setups:
Onboard Digital Out: Realtek 2.12, 2.14
drivers) No crashes but Framerate with on-board was lower than PCI card, despite both cards using software based decoding
Auzentech Digital Out: Pc freeze/sound loop/BSOD
Auzentech Analogue: DTS or DDL enabled caused crashes much quicker than using 44khz PCM setting. However video files, music and Fallout 3 seem to be exempt. Far Cry2, COD4, COD5 tend to either freeze/crash with stuck sound loops or BSOD. Farcry 2 tended to freeze the PC or CTD with un-killable stuck sound requiring restart while COD tended to BSOD. Possible EAX +
driver incompatibility?
Repeat offender in auzentech digital/analogue crashes/BSOD = cmudax.sys (C-Media driver)
Tuner card installed/uninstalled + swapped ports: No difference.
In seven, the auzentech shares IRQ 17 with the atheros LAN. Same as in Vista, which runs flawlessly (IIRC).
So basically I'm back where I was with 6801. Poor drivers.
I haven't read about any significant changes (or any for that matter) to Sevens audio stack which could account for the broken driver
At least FO3 and video works without the x86 crackle