You need to know what kind of cabs and bass along with the kind of tone you're looking for before much can be said about settings. I play rock, funk, and blues with either a Valenti PJ5 (alder/rosewood) or Carvin SB5000 (ash/maple) through the SM12.0 and an Uber 212T cab. For both tube and FET channels, I run the pre-gain at 12:30, volume at 1:00, master between 11:00 and 12:00. EQ is very close to flat and I get a nice full sound; fat but still tight on the bottom, nice low mid punch, articulate mids, and a little air up on top. This seems to sit well in the mix. I usually play a little behind the neck pickup but shift hand position and attack as needed for the song. Pickups are usually balanced or within 1/4 turn of each other to give the tone I look for. This is only one player's take but thought the context might give settings a little more meaning. Don't let the knobs intimidate. Set everything flat, get the gain structure right, then tweak some EQ to taste. A little goes a long way.
