Hey Freshcuts, I had the same problem with the same Motherboard as you and stumbled on a solution that made my sound work in Leopard 1.5.2:
In the bios configration disable the IEEE1394, enable the AC97 Audio BUT disable the game port and the MIDI Interrupts (AC97 = Enabled, Game Port = Disabled, MIDI Port Address = Disabled, MIDI Port IRQ = Disabled).
Once this is done, your soundcard should work with the AC97 Kexts you already modified, if not I will upload the kexts (with codecs) I installed on mine.

I hope this will help anyone with such a problem.