Rene,
I used to do a "Dualing piano" thing that required pretty loud amplification of the music, so we gutted 2 grand piano's and replaced the "innards" with digital Korg pianos. Really helped alot. The hardest part was taking the harp out of the case (HEAVY, clumsy).... the rest is just nuts and bolts.

I've also seen pretty successful "mockups" made of plywood tops with curtain sides that fold out of the way for travel, and just hang to give the apearance of wooded sides. ............ actually looks ok!