Have you tried using acpi=off on the kernel boot line? pci=noacpi alone didn't give me joy and caused my 3com card to go out of whack every now and then...
The major merge in 2.4.22-pre is the new ACPI code. BTW, I'd also suggest updating to ALSA 0.9.5, since the SPDIF actually works on that ;-)
If you want your PC to turn itself off, you'd need to go back to APM though... UGH.
I think it might be the PCI IRQ routing code in ACPI that is seriously busted. Mmmmm. NVidia kernel gods? Are thee around?
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