I am also using a Mustang one and to get the clean sound with some crunch I am using the red on british 60's. Try to play around with the gain and volume depending on how much you want it to break up.
If you go into fuse you can also change the settings on the compressor. I love this sound for blues and also some of the Hendrix songs.
One more thing I am trying the new Slinky Cobalt strings and they made the crunch sound cleaner, it took out some of the mud you can get with distorsion.
Good luck
Lars
Lars