Can the Montage layer two of the same piano voices (CFX, Bösendorfer) at the same time to create a more dimensional piano sound?

You can layer MONTAGE pianos, of course, I’m not sure I would characterize the result as being “a more dimensional piano sound.” But certainly any number of Parts, up to eight, can be combined in a keyboard controlled Performance. Since the CFX Concert, and the Imperial Grand are four Part and three Part Performances, respectively... you could layer them. The results with two of the same piano layered is not multi dimensional, but probably just detectably louder than playing one alone... and possibly a little phase-y.

Sure, you can play both at the same time, but please do so because you think it sounds good, not because it sounds like a ‘good idea’ or because you think it sounds ‘expensive’. There is no harm in trying, but you’ll probably discover why that is not a Factory Preset. You be the judge!

Certainly, two *different* pianos would likely give a more “interesting” result versus the same exact piano. But even then, it might sound more like an argument than complimenting the sound of one alone.

There are many examples of the combination of acoustic and electric pianos, (a sound used often by Stevie Wonder, Darryl Hall, and others on countless hit songs) in the MONTAGE Factory Set... including Performance number 1... “CFX + FM EP”
“Upright Mod 1” - Upright piano and a FM reed e.piano
“Upright Mod 2” - Variation of above
“Upright Atmos” - Variation includes string and pad remove with MW
“FM EP & CFX Grand” - a 7 Part version of the original, with string on AsSw1

Use the [AUDITION] button to observe how the piano, electric piano and pad/strings are used.

Try your idea of layering two of the same, while that sounds good on paper, in reality, not so much. Phase-y, boomy, wierd, nasal... like a piano with a head cold ... you decide.

If the question is how to “merge” Performances you can learn about in the article on Category Search. See the paragraph heading: “Performance Merge”