Hello Allen:
I'm confused by "Artisan Operating system". Do you mean the keyboards, stops, pedals, and swell are using Artisan uMidi input and processor boards for MIDI encoding? Also your question is fairly broad as it would be helpful to know the basic genre of music your planning (Baroque, Classical, Hymns, Theatre, etc.) and the sample set or sets you will be using or purchasing. There are some sample sets available in surround sound where you'll need a minimum of 4 channels (front and rear) to take advantage of the sound reflections.
Regardless of all that, try the advanced forum search using "multi channel" as the search string and you'll see lots of excellent posts on this subject. The great thing about HW is you can get a lot of mileage with just 2-channel stereo using full range speakers or pro-level headphones before venturing into the multi-channel arena.
Danny B.