I'm not clear here whether you want to use the keyboard for note/chord entry, or use a synthesiser as the sound generator, to make the sounds instead of BiaB.

If its the former, you will probably be able to set up the synthesiser to send MIDI to BIAB. Most, probably all, recent synth keyboards will send MIDI over USB.

If it's the latter, then BIAB probably has to send MIDI to the synthesiser, so RealTracks probably won't work unless your synthesiser can also play audio sent via the USB, i.e., operate as an audio module.

Jazz relative beginner, starting at a much older age than was helpful.
Kawai MP6, Korg M50, Ui24R, Saffire Pro 40.
AVL:MXE Linux; Windows 11; Win8.1: Scarletts
BIAB2022 UltraPAK, Reaper, a bunch of stuff.