I would start with input off, output, bass, mid, and treble straight up at twevle o'clock, presence off and blend maxed out.
Bring up input slowly, listening carefully for the amount of drive you are getting - do you want growl or clean?
Then bring up your output to fairly loud.
Still resisting the eq and presence knobs, work the input and blend controls first - remembering a little goes a long way. With my G&L. the input ends up around 9 or 10 o'clock, which gives me a slight growl on heavier playing. My blend is in the 1 or 2 o'clock area.
Finally tweak eq slightly. For me, I run very little presence, about one o'clock on bass, mid varies from 11 to 1 o'clock, treble slightly less that 12 o'clock.
I run a Symetrix 501 compressor in the effects loop.
If you are not getting enough gain, try any input you can on the amp, input, effects return, aux in, power amp in. Gain has never been a problem for me with any Sansamp product, in fact, I have trouble taming the input section for a cleaner sound.
Hope this helps,
Mark