@shastastan:

This statement: "For whatever reason, I am unable to render directly to mp3 with BIAB or RB could be due to my ext synth setup. "

This is not possible with ANY DAW. What you are asking it to do is convert the analog signals from the analog outputs on your external synth, into digital format, while mixing and converting to .mp3.

This is not a feature of any DAW software.

You first have convert all signals to digital tracks in the DAW software. If you are using a soft synth (of which there are legion different types - you are referring to a general midi synth of some type in Mixcraft), then it is possible for the computer to convert MIDI data into a digital track on the fly.

With your external synth, however, you have to RECORD the output of the external synth into a specific audio track(s) first. Then mix to what you like, then render to .mp3.

-Scott