Piano Forum

I agree that's a lot to look at, and thanks to quantum for giving an up-to-date précis.

The last time I had set up a DAW, it was under Cubase SX, and that was more for editing band performances, and as one of many hosts for softsynths which, at the time, were barely adequate for even Hammond Organ+Leslie speaker, or Fender Rhodes, or other basic keyboard sounds.  At about that time, it seemed composers and arrangers I knew seemed to favor Sibelius's various products for reproducing orchestral sounds from a score or via MIDI.  I think the world has moved on a bit.

I am curious if the OP wants a backing track, or, as in the initial plan (as it seemed to me), to have a second pianist provide the accompaniment in real time on an acoustic piano.

I don't think it's unrealistic to hire a second pianist, or, really, a keyboardist in this case, to reproduce the orchestral score in real time.

You might have to pay them extra to get good at using the various MIDI functions (on, no doubt, a machine capable of dividing the keyboard into different zones, and different sets of discrete groups of "instruments," which should be well within the capabilities of even a modest controller keyboard).

It could be done, though, and certainly has been, in real time.  At least with an adept accompanist.

I wouldn't think a backing track would be all that effective, or give the best display of your interpretive efforts.

ETA Yes, it's possible, and AFAIK, it's always been possible to indicate to the backing track little changes in tempo and dynamics.  It could be done via (yet another) pedal, or a breath controller, but I don't think that's reasonable.   For example, I know a few jazz guitarists of good reputation who use backing tracks, recorded by themselves, but they have at least half-dozen pedals set up (not all the backing tracks:  you know guitar players, they like their effects!), but they seem to manage.

Like you, the people I know who play live with backting tracks have their set lists figured out, generally, use various pedals (or even one single pedal with some lateral motion, like in those old "home organs," to control at most a few aspects of the backing accompaniment.

I don't think that's what you want.

Then again they only got six strings, and unless they have 1958 Les Paul sunburst, they don't have sustain, either. 

If it's not a live performance, I'd just play to a click (more or less) and add the overdubs of orchestra in post. 

If live, any pianist could pick up the rudiments of doing the orchestra, pretty sure.  Given some practice. 

But you'd have to pay them more and there's a learning curve that's steep, playing different zones on the KB, and swapping the right patches at the right time.  Those kind of people aren't so much piano players, at a given moment, however much they can play, but they're good at doing that kind of stuff.