welcome fritz, a few comments ...
i'd rather consider to setup 2) than 1) the noticeable difference for the DAW would not be as big as for the sampling machine (altiverb instances might have to be added to the math)
there is no big difference with server boards - except you need a 64bit OS for more than 4 GB RAM and XP64 is almost the same as XP32. do not forget server RAM, especially if you want more than 16 GB will become the most expensive part of the hardware.
from what i heard and can say the Pro Fire works better on win than on mac (and i'd assume you should put each on a seperate FW-controller ...)
but why not looking after an apogee - best choice for a mac IMO regarding latency - in any case a solution which sits directly on the PCI bus instead of having again FW between (adds unwanted CPU load)
christian
and remember: only a CRAY can run an endless loop in just three seconds.