Doc-Z, I was not thinking of you when I said cheesy, but I've read elsewhere in this and other fora that some find the styles early Casio-like. Sorry if my reply felt that way! BiaB have come a long way and yes, I think their patterns repeat themselves, but where Yamaha repeats every two bars for the most part, BiaB styles varies randomly, meaning it is less repetitive than you think, even though there is only an A and a B part. I have not tried to use it as an arranger but it can make styles out of any midifile. Don't know about the Yamaha mega and SA voices though. The man to ask is Simon at SVPWorld, he is an expert on midi and Yamaha style building.
http://www.svpworld.com Roy-Andrč