Dox, it's obvious from this post you're not a noob at this so here's a more pro level suggestion for you. Forget Biab but upgrade so you can get Real Band. RB is a hybrid of PG's long time sequencer Power Tracks and Biab. I'm not going to post a whole description of RB, you can do a forum search for my username and you will find lots of posts over the last 6 weeks or so where I've gone into detail about it plus you can jump over to the RB forum and read all about it.
The exact point as it relates to your situation is this: You want to create a piano track to go with what you've already laid down. In Biab you can select a style, pick a RT or midi piano part and generate the tune but you have to do the whole tune and it get's very confusing after a while trying to remember which version might work out the best. In RB you have 48 tracks, it's a standard DAW in that all your NI plugs work plus it will generate Biab parts both RT and midi but the really cool part is you can generate your piano part using a single track at a time and everything else stays as is. This means you set up the chord grid, put in your part markers and generate a RT piano part. Then click on the next empty track and do it again but you could change the style, put in some chord subs, change the part markers. Even if you used the same RT you will get a different part. Then do it yet again on another empty track, this time try a midi piano part with a different style using your NI piano. See where I'm going with this? RB will only generate one track at a time if that's what you want. You can create many separate tracks using different RT's, different midi styles, chords, part markers all to give you a ton of choices in order to start cutting, pasting, creating loops all that stuff in order to make one good piano track out of all those test tracks. RB is a full fledged audio/midi editor. I normally use Adobe Audition for wave editing but during the RB beta testing I stuck to RB just to see if it really can do the same job Audition can and it does, it's just the workflow is different but the functionality is all there.
I've done this sort of thing using both RT's and midi guitars and Real Drums plus midi drums using my Jamstix kits. When you mix these together and you have a good sample for the midi, it can sound very good if you're a decent engineer.

Bob

Biab/RB latest build, Win 11 Pro, Ryzen 5 5600 G, 512 Gig SSD, 16 Gigs Ram, Steinberg UR22 MkII, Roland Sonic Cell, Kurzweil PC3, Hammond SK1, Korg PA3XPro, Garritan JABB, Hypercanvas, Sampletank 3, more.