I don't think any number of Quads will be able to play orchestral music convincingly? (question mark since I can't say since I've never heard anything other than a single pair). Or even solo keyboard music experienced from the first ten rows. One of my favorite solo keyboard concerts was hearing a recital of Schumann, Rachmaninoff, Schubert's song transcriptions by Liszt, and the most beautiful Aria from GV.
From the 3rd row the power of a concert grand is simply remarkable. I don't have the vocabulary to describe those sort of religious experiences when sound and performance match up. I don't think that too would be capable on any number of Quads, the dynamic range is too great.
And what about comb filtering and frequency cancellations when you stack panels like that?
(any solo keyboard lovers, if you have a chance to see Sergei Babayan, do not miss it! For me one of the greatest current recording/performing pianists)