I'm using a Motu 828 (not mk II) from time to time to do live recordings, with a Fostex AD-convertor for ADAT, and I use whatever's left (mostly bypassed FX) to convert two channels to S/PDIF. That way I have a total of 18 analog in.
I've used this with several desktop and laptop PC's, and never had a problem. I even used it with a cheap Firewire card with the NEC chipset in it! Worked flawlessly.. According to MOTU's website, the only problem with this chipset is the functionality of the footswitch (punch in/out). Although I don't use that function, I gave it a try, and it behaved properly...
stike I DID have difficulties when combining the 828 with an external firewire HD. When I switched to USB2.0, all problems were solved. But I suppose that has nothing to do with the 828, I think it's more of an issue with this cheap HD...