Have fun with your new amp! Don't be afraid to experiment. It's not as mysterious as it might seem at first. If this hasn't already been mentioned, advancing the "Send Mix" knob adds a bit of unique sound quality all its own. A little bit is usually more than enough.
The settings of the "Pre Gain" and "Post Gain" controls also have an effect on the sound. Higher Pre Gain settings tend to give a fatter sound. Higher Post Gain settings give a little more open or airy sound.
This is all very subjective of course, so don't afraid to experiment. Personally I use the EQ very sparingly, and get the sound I want primarily with the Gain and Send Mix control settings. Although I do use Bass, Treble and Mid if I need them. They are very effective.