Honestly..., I'm with Donny here. The S900 has some great trumpets, saxes, and that sweet violin is pretty nice. Have you considered using the synth function on the 900 to fine tune those instruments? It may save you some money. If you're not too familiar with editing those parameters just drop me a line and tell me what you're wanting from them. I may be able to give you a few tweeking suggestions.

As far as modules go...., you may want to look at the SonicCell.., maybe a used Motif ES rack, Perhaps a Ketron SD4....