Great question - and that sounds like a great combination to me. Looking forward to what comes from it all.
There's a lot to digest with the new tools but to me, this can't be overlooked..
Transpose a layer or two! to get something cheeky like a pretend 12 string piano (or harmonies - or for microtonal works, could be fascinating with transposing for effect - setting that up to MIDI control.. pedal to toggle harmony - AH! That's not something I've tried yet - but way out possibilities everywhere).
Or staying a little more firmly in realism with the older pianos..
Using the same instrument for all 3 layers with different tweaks and reverb settings mostly so far but have had a few multi-instrument experiments which have been promising.
Going a little further into new pianos inspired by real pianos, here's the first thing which came to mind for 2 era pianos - almost any of these for a main layer. I like quite a few of those older ones like the Square pianos along with the Neupert clavichord (with that bebung!) for a second layer.. tampering with hammer and various things.. it's giving me something 'nearing' one of my fav Iberian piano.
Tried transposing down the clav, and added the old Besendorfer transposed up 12.
Different reverb and settings for each (layer 1 normal-ish.. layer 2 short everything for the close clav (cabinet kind of tweaks), and longer singing higher strings low in mix). Kind of dreamy sounds inspired by the lone instruments - found this highly absorbing.
This is addictive - so much creativity is going to come from these new tools.
Yeah agree @aWc - the Steinway B and others mentioned - lovely tones.
Today I'm diving into a Steinway D and Bluthner morph - really liking this combo.
Pianoteq Studio Bundle (Pro plus all instruments) - Kawai MP11 digital piano - Yamaha HS8 monitors