Gotta get the EWQL Larry! First I have to make sure the IMac can handle it. I think the Platinum samples are around $800 (Wow, 68 GB Free Hard Disc Space). I don't see a piano on the list of instruments.
http://www.majormusic.com.au/products/ew_so_pro_xp.php

Requirements: Mac OS 9.2, OS 10.2.6 or higher, G3 500 Mhz, 256 MB RAM 68 GB Free Hard Disc Space (for the four volume collection - individual volumes are listed separately), DVD Drive

I'm okay up to here (not sure about the compatibility): MAC (VST®2.0, ASIO™, Soundmanager™, OMS™, Audio Units™, Core Audio™, **RTAS™)

Best, John