Re: tracks
In your case I think you would want to create a multitrack wave file for each song to make sure everything stays perfectly aligned. In fact, if the stereo file is a band mix, you might allow yourself some additional control by rendering out a multitrack version (kick,snare, stereo drums, bass, guitar L, guitar R, lead vocal, back vocal L, back vocal R, click, etc..) up to 16 tracks that all end up being one file. Easier to manage & would allow for whoever is dealing with the audio some control that a stereo mix doesn't.
Re: RME
To be clear, in the case of a Fireface 800 or 400, "pre-amps" would refer to the mic preamp inputs. Since the questions you have asked all relate to audio playback, you would be using line outputs & not preamp inputs unless you will be mixing live audio with QLab playback. If you don't have one already, note that the RME Fireface 800 has (8) TRS line outputs & you can also use the headphone output as 9/10 unbalanced outputs. Add (1) or (2) ADAT i/o devices & you can have 8 or 16 more ins & outs.
If you have an doubts about your concept, you can rent whatever licenses you might need to accomplish your goal by the day to test everything.
rentals are on the right hand side of the page.
Let us know how it all goes for you.
Best regards,
ra byn (robin)