Hey I've tried almost everything so far, I can't get the onboard audio to work on my K8N Neo2. I also have a sound blaster live! but as far as I know that doesn't work no matter what.

Did you bother to replace the Audio Out Cable, from the Sound Blaster Live! to you ALC655 (AC97),
*Edit* AC97 on K8N Neo v2 (ALC655) Works outa the box. Sadly Core Audio is a different story.

As you point out the Sound Blaster doesn't work with Mac OS X.
Allthough the ALC655 (AC97) does work I have never gotten it (Mac), to recognize it in the System Profiler (10.4.6, 10.4.7 & 10.4.8), do not 'see' the ALC655.
Allthough Sound works in 10.4.x, Core Audio does not, so I can't get Sound in 3D Games (Doom3 - Quake4),.

I'm also currently looking for a new Mac/Windows Soundcard.
I was thinking of the Terratec Phase 22, A PCI Soundcard which works in both Mac and Windows. The card is simple and Profiler plentiful enough on eBay.
But, I was wondering if anybody had any oppinions about this Card?

The drivers from terratec dont work under 10.4.8 and in XP/Cubase it has a fairly high latency (10-20ms)

I have the same audio chipset in my rig and I got the spdif out working in stereo (it's not 5.1 but it's something) by replacing the device an vendor id in the ich7 and ich8 sections of applehda.kext with the id's for the ALC655 I dont know if that would help you with core audio but you could give it a try. I haven't heard anything about that soundcard. I just ordered a m-audio usb transit.