WOO-HOO!!! Definitive answer for this particular scenario is - do all monitoring from the XV headphone out. There was a MIDI driver latency setting that was leftover from some other device config, I set it to zero and now everything is GREAT! I set BIAB to use Roland XV-2020 IN and OUT connected via the USB cable only (no 3rd party MIDI/USB adapter), and play a BIAB song that I've input chords for and hear it from the XV's sound processor, along with my EWI MIDI IN to the XV (recorded as Melody track using a patch selected in BIAB) in perfect sync. I then stop recording and play it back, hear it all perfectly in sync, and can generate a lead sheet showing the chords and the melody that I just created in perfect notation. This is what I was trying to do using Finale Songwriter, but the MIDI input notation was horrible. You get so much more with BIAB!!! ...if you can figure out how to use it all.

The crazy thing about all of this is that there are so many different pieces of equipment, drivers, configuration settings, and ways of doing things in BIAB (lots of nerd knobs on this puppy) that you could probably achieve some success using several different configurations and methods. The trick is figuring out which way works the best for your specific collection of gear and what you're trying to do - which seems to pretty much all boil down to trial and error (LOTS of both). Mission accomplished, thanks for your help!