Rikki,
I too have the Drums on Demand CDs and agree that, by comparison, BIAB is a real bargain; however, the DoD loops are really good and I am thinking to use them to create my own BIAB "Real Drums".
Speaking of sound sources, in the past I never worried about them and have always used the PC soundcard (Creative Audigy Platinum). However, the Real Drums are so good that for the first time I feel the need of more sounds of the same quality. My choices presently are: either one of my modules (Yamaha Motif ES rack, Fantom XR, Ketron Midjay) or hook the PC directly to my Tyros 2. I assume that BIAB will send the correct program change numbers for every style and they should call the appropriate sounds within the GM bank: am I correct?
However, I don't think that I will need more than a bass and maybe a rhytm guitar. In fact, when using a style, I am always afraid to use too many rhytm tracks, for fear of sounding canned, so I tend to keep the base to a minimum.
Ciao!