I suggest you plug straight into the amp, turn the volume closest to the inputs all the way up, and turn the master volume (next to the on/off switch) up fairly high (if you can handle it). That's about all the distortion you'll get out of that amp. If that's not enough (probably not, going on your previous posts), I suggest you get an overdrive pedal such as a Tubescreamer, Boss SD-1, or an MXR ZW-44. Plug your guitar into the pedal, and then from the pedal to the input of the amp. This is what I do with my Peavey classic 50 when I need more gain. Doing this will give you raw, unadulterated, nonprocessed, in-your-face rawnchyness that no processor can give you.

And for God's sake, whatever you do, don't cut/scoop out all the mids!