I have been using Key Rig for a few weeks now..
One of the things I like about the M-Audio program..it allows me to run all 4 modules at the same time, substituting a sound from the GM module with a sound from the Piano module, a organ from the organ module and a synth patch from the synrh module..to any channel within the GM module..
I have been able to play the other modules from a keyboard , but not the GM module sounds[yet]..I will check it out further on this issue..
Although the drum kit is nice ,I would have liked options for kits like the TR808 etc.

Overall I still like HyperCanvas better, but still would recommend KeyRig..