Aidan, you make a point that some overlook. It demonstrates the importance of room acoustics on sound, an issue well known to buyers of acoustic pianos, which sound wonderful in the showroom and less so at home. It also illustrates the realism of the Pianoteq models: the sound of different instruments changes in different ways to the change of room acoustics.
I have experienced the 'acoustic piano' issue. My last Kawai grand was greatly improved by a day's work by a Kawai master piano technician on site. Re Pianoteq, I have re-tweaked instruments after moving house and also when moving up from PT5 Standard to PT6 Pro. We are very fortunate in having a product that we can change to suit different circumstances without having to pay for technicians.
One further point which illustrates the realism of Pianoteq. I have played many acoustic grands, privately and publicly, so can adapt quite quickly to different instruments. I am aware of the same need in switching from one Pianoteq piano to another, if I have been playing one for several days it takes a short while to adapt to another.
Re the B versus Grotrian, I was very impressed with the B when it appeared, then even more so by the Grotrian. (In PT5) It really seemed as if a technician had done some work on the action. (I have a Kawai ES7 - not the most sensitive of digital "actions" but good enough) The Grotrian in PT6 is smoother, more integrated, a warmer sound that suits Romantic music. (I am exclusively a classical player) Coloured, yes, but colouration I like. I struggled to get a good sound from the new D, but now enjoy Haydn, Mozart, Beethoven on this, having used the Pro spectrum facility to fill out a slight hollowness around the octave or so above middle C. Not a criticism of Pianoteq, again an adjustment to the acoustics and my sound system. I'm not sure there is a niche - for me - for the B now I can enjoy the D.
Hopefully Aidan you have at least PT Standard and can tweak the sounds appropriately.