Although I'm a newbie to BIAB, (love it) I've been using the freeware Audacity for some time and it's good at converting to a range of bitrates in MP3 or whatever. I've also been exporting my BIAB tracks into Audacity to do multi-track vocal recording. (Then correcting my warbling in Melodyne- there might be a better way than all this exporting and importing but that's my process for now)

Audacity is a free, (open-source) cross-platform digital audio editor and recording application. It is available for Windows, Mac OS X, Linux and BSD. Great program, new version just came out.

http://audacity.sourceforge.net/