Zeke,
You have mentioned two totally different scenarios.

BiaB is playing notes you'd like to change
VS
Using your MIDI keyboard synth for bass sound

This is the classic Audio vs MIDI ..

Clarify the first (highest) priority;
do you want to hear your MIDI keyboard synth play the existing bass notes
or
do you want to change the notes that you hear the current bass playing in BiaB
or
both?

I do not work here, but the benefits are still awesome
Make your sound your own!