Looks you have firewire audio interfaces? Could be the firewire controller on your mother board. I've seen time and time again people having problems with motherboard firewire controllers and seen this first hand on my friends pc. He had a much newer i7 machine then me listed in my specs but performance for me was much better. I installed a Ti chipset firewire card in his pc and the problems went away.
Sorry if this has been mentioned. I always just skim through threads and sometimes repeat things other people have said.
But anyways, if you are using the motherboard firewire, or even a non Ti firewire card, you may want to replace it with a Ti chipset card to see if performance improves. Think I paid like $50 or somehting.