You don't say what flavor of Linux you are running, but assuming
that your using a stock redhat kernel then one thing you might like
to try is turning on IO-APIC support. One of the things RedHat does
for stability is only use XT-PIC interrupts for Uniprocessor systems.
The latest 2.4.18-17.8.x series allows you to compile IO-APIC support
for UP systems. This might allow your chipset to use PCI IRQ routing
which has up to 255 possible IRQ values rather than the default
XT 16. I have an AMD board at home (Gigabyte 7VRXP) which when
I use UP IO-APC assigns PCI cards up in the IRQ 16-20 range, just like
PCI spec says it can be rather than the antiquated XT standard.
Hope that helps,