firewire problems - help!

hi!
firewire audio interface (focusrite saffire pro 40) has been acting up, crackling sound, performance down nothing..
realized, affected whole system - not audio performance.
problem goes away when disconnect sound card. connecting different firewire audio interface causes similar problems - not same thought (confusing.. know.. different chipset?)
bought pci-express firewire card 3 firewire 400 ports - 1 said compatible mac pro (exsys ex-16500e using texas instruments chip) - insert in pci-e slot (no matter 16x or 4x) - mac doesn't start anymore..
wondering if make sense try firewire 800 - 400 adapter.. since it's cheap.. work or cause same problem.. e.g. 800 ports damaged if 400 didn't work?
problem occurs on both - rear , front firewire port...

i'm bit helpless.. don't know inner workings of mac.. can help?

i'm working on 2008 mac pro, 8x2,8 ghz, 16 gb ram running os x 10.7.2.

did fresh install of lion , programs/drivers (formatted hard drive completely) - sure - problem sticks around..

help/recommendations appreciated!
lot
cheers
gernot

 

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