As PCI cards can only be fitted in pre-intel macpro (first gen) and earlier, I don't think the driver has been updated to 10.6 (and It won't be).
IMO, forget about your Delta stuff and buy yourself a good interface with the money you saved building a hack instead of buying a mac.
One of the good things is that you won't have to worry about the sound when you configure your system (I deactivated the sound in the bios). You'll only have to install the OSX driver (if needed)
known as good FW cards on mac :
Presonus
Motu
Echo
Focusrite
TC Electronics (avoid second hand on the SK48 - except if you know your seller because of problems on the preamp section on the first gens, the others are fine)
RME
Lynx
Apogee
Some requires a driver (provided) and some work out of the box. Check out the reviews but if you pick up you audio interface from this brands, you shouldn't go wrong.
If you want to stick to internal cards, then you should consider PCIe stuffs but it's far more expensive (almost only high end solutions)
RME
Lynx
Motu (note that you can find PCIe "relatively cheap" solutions on this case)
Apogee symphony
Avid (Protools HD)
I own myself a TC Electronic Konnekt Live interface which works perfectly on my all new rig.
Check out the thread for the detailled specs :
http://www.tonymacx86.com/viewtopic.php?f=43&t=6620&start=10
