There's anew soft synth/sampler coming on the market real soon. Garritain personal orchestra with a player called aria. It maybe the best, lest expensive way to get high quality instruments.
If you go to the Northern Sounds forum, there's a sub group on the GPO instruments
http://www.northernsounds.com/forum/index.php?
From the limited info, it looks like the program that manages the sounds"Aria" maybe very compatible with BIAB.
There are also several free soft synths and a site I find very useful for that info is
http://www.kvraudio.com/
Hope this helps
Wyndham