Nik sent me this awhile back. This might be a dumb question, but on the clean channel, what happens if you run the master wide open and the first volume lower like one would on another amp with a master volume to get maximum cleans?
 
1) For max cleans, master is low, but volume set high.
 
    Indeed, the amp is quirky this way.
 
   So set your master at say, 11 o clock, while your volume, at 2 or 3 o clock. You will get most clean this way.

D*mble style Master Volumes aren't as intuitive as a typical one.

For maximum clean headroom on the clean channel, the idea is to set the Master Volume around 11-12 o'clock and the Volume between 12-3 o'clock.

If that doesn't work, it would't be a bad idea to double-check bias.