Hi James.
I'm glad you've discovered RMX!
Don't just limit yourself to just drums in RMX. You can really put anything in it. Record your own guitar licks, REX them and stick them in RMX.....bass lines, individual hits, fx, vocal things, piano, string lines.....they all are great to have in RMX because they can be pitch shifted, reversed and MUCH more very very quickly. And anything pitch shifted is done in real time on a slice by slice basis which is cool. Plus anything tempo based that you add to it will always lock to the tempo of your tune.
The Back Beat and Burning Grooves Xpanders would be a good starting point for rock stuff. And those grooves are particularly cool in RMX because you can use the Chaos Designer to subtly or not so subtly make the loops improvise. Also, I just bought that Total Rex from Zero G....wow.....so much stuff in there....your head will spin.
Anyway, I HIGHLY recommend watching all the videos you can find on RMX at the Spectra site. It's worth the time spent. Edit Groups are a little mysterious at first, but once you see them in action, you will find them VERY useful.
Cheers.
-gabe
(For the record, I have to mention I wrote the user's guide for RMX and beta test for Spectrasonics. I also wrote a short article for MIX mag regarding RMX....you might find it useful as you continue exploring the world of RMX:
http://mixonline.com/mag/audio_spectras ... index.html )