So, the PZM inside the "chamber", so to speak? Interesting idea!
I'll add a technique I used once, with interesting results.
Hung a mic from the ceiling above the piano and gave it a push so it swang (is that a word?) back and forth over the top while taping (watch the wall!). Gave some variance to the tone and volume, almost a Leslie effect but much more subtle (is that spelled right?). Can also be done in front of an amp...