Well I use FW 31/32 as my main stereo pair from the DM4800's mic out, and so don't have them come back into a channel (feedback potential!) I bring the output of those tracks back into a monitor select button. I route/record the mix output of the DM4800 to those tracks, using input bypass so it goes direct from the stereo outs to 31/32. If I am mastering in Cubase whatever that's always the stereo master tracks out, and I just punch up that monitor select in the DM4800 to hear what I am doing,
Also the channels have Mic/Line on the inputs, and the corresponding firewire card outs on the return side. I also route the mic/line inputs on the console using input bypass to go directly from the mic/line to the firewire card - a clean record, before the channel eq et al. On location recording, I can record the rehearsal, and then switch to the channel return inputs and continue to tweak my mix when the band breaks before a live show/broadcast/webcast. SInce I haven't printed the eq or comp, etc, it sounds the same on playback as when recording.
Of course there are many ways to do things!