You might look into getting a Redbox Cabinetulator for about $100 (or about $50 used)
http://www.wicasta.com/music/gear/mk2.html

It goes into the send/receive of any effects unit and does a great job of eliminating that 'cheese' sound from most overdrive pedals.
I've been using it on my Boss ME-5 for years and couldn't do without it.

Another option is to use Amplitube. You can get a decent simulation of just about any amp/cabinet combination on the market including Marshalls JCM's, Fender Reverbs and AC-30's