It takes awhile to know how all the mini switches effect the EQ and Gain, but once you do, you'll like the amp even more.
For max gain, set the switch above the gain knob to the hotter setting, set the structure switch to the hotter setting, turn on the boost, make sure it's in modern mode on back panel, and if you want more bite, use the assignable presence switch for the red channel and turn it up. That will put the gain at extreme levels like a Uberschall.
A couple things you should know.....
If the boost is ON on the head, the LED and boost are defeated on your footswitch...it's not broken.
You can assign either the blue OR red channel to plexi mode, and it defeats all the mini switches and simplifies the circuit. That means you could use the blue channel as your highest gain and the red channel as a plexi, or visa versa. The switches won't effect whatever's in plexi mode.
The assignable presence can be off, 1st channel, or 3rd channel. If you want more bite out of the gain channel assign the presence to red. If you want more sparkle on the clean channel, assign it to green.
The FX loop output knob is great for getting the amp to sound better at lower volumes.
I usually keep all the cabinet damping switches to the neutral/middle position.