That new Roland RD700GX sounds amazing, but I know it is way too heavy for you (don't want to end back where you are with a hernia, too!)...

You MIGHT consider a Fatar or M-Audio (or your choice) 88 controller, and get a Sonic Cell. That's got a seriously good piano in it (sounds like my G70's one), plus SRX slots for their SRX-11 and SRX-12 Grand and EP expansion cards. SERIOUSLY good sounds, IMO. Plus, you could add it to your S900's arsenal when you don't need the 88... Food for thought (at least, better than hospital food!)

Get well soon...