If you just dial the mids down by themselves it'll kill the amp's dynamics.
I run the amps mids around 12:00 or higher, then use an EQ in the effects loop to scoop the mids out.
The other way is to turn the treble down to zero and turn the presense up to taste.....
If you're playing in a band you'll have to put alot of effort into tweeking your EQ so that you still get some cut, otherwise you'll suffer from "dissapearing guitar syndrome".