In the past I only used my M80 as an "amp" at practice , so I wouldnt have to transport a real amp. Works great plugged direct into a mixer channel. But recently, I used it inline w/ my signature rig, and I must say, it really was an improvement. With my GK mostly set flat, here are my M80 settings:
Clean Volume: 12:00
Volume: 12:00
Dist. Blend: 7:00 (or off)
Trigger 1:00
Gain :12:00
Color: engaged
Gate: engaged
Bass:11:00
Mid: 1:30
Treble: 1:30
Distortion

ff
Effect:ON
These settings gave me rich , strong lows, very present mids, and sparkling highs, thru my passive Fender Jazz. It also seemed to compress my signal a bit, which sounded better and punchier.
Please post your fav. settings for the M80 and why. A great piece of equip. Best backup amp for the $ and it will fit in your case.