The first thing I would check is the RAM, I had issues with RAM module incompatability when I upgraded to a non Apple processor. Remove it all and add back one stick at a time.
I have a question about this card if anyone has it or knows anything about it. I've been getting random freezes and I've been trying to pinpoint the problem, but it just never seems to show. At first I thought it had something to do with the USB devices due to whenever I load something that uses USB it freezes or maybe it was a VIdeo issue due to when i do too much video applications it would freeze as well. I've put a new heatsink and fan on the sonnet card, but it doesnt seem to be heating up so I dont think its that. THe other only thing I can think of is it being a memory problem due to having a mix of memory chips like some 32's and 64's.