I'm curious about your setting Master at 3 o'clock, and how it affects the sound. I've always stuck to the manual's recommendation of leaving Master at 12.
The input level controls the level of the signal at the input stage of the preamp. The master volume controls the level of the signal at the output of the preamp (at the input of the power amp). Set the master control at “12 o’clock” and the input level at zero. The input level should then be used to control the overall output of the unit.
In my two outdoor gigs so far with the DoubleShot, I've also boosted the mid and highs slightly, left the high pass filter off, and set the DoubleShot on the ground. Everyone (audience, bandmates) have made positive comments about the sound, and I've never heard myself better.