Basically rectostudioguy, the studio preamps tone controls, are pre distortion. So it does really need a pre input eq. Rectos however have the bass mid treble after distortion like marshalls. There it is more usefull. I never really liked my studio pre boosted. Or the triaxis or my f-30. The same if not better (for me definately better) results come from carefull eq adjustments.
Anyway, why not have the input volume at about 6-7, the lead volume dimed, and treble pot at about 7-7,5 with mid and bass to taste (although keeping the bass low is usually the canon in these preamps). You will get plenty of gain for legato with a humbucker guitar. Also the fat switch adds more, so does the bright one. If you think the heavy rythm tone will suffer and become mush, try rolling back your guitar's volume knob to clean it up (more so like having the lead drive to 3-4...).
Slamming the input with a much louder signal, (boosting) does not necessarily mean an immediate increase in db, it usually does not. It will change the way the preamp distorts. The volume increase you ask for your solos, as the abilty to cut trough will come from an additional volume boost that might be better to acquire after the distortion mainly in the loop, using your g-major with another patch with higher volume and more mids.
Your studio preamp is essentially a two channel amp. And even then compromised due to sharing the eq controls. So it is difficult to turn it in a three channel...
If you could manage to play rythm, hard rock rythm or metal without the graphic eq engaged (try it, you may find it it sits nicely in the mix, althougn not scooped) you could use the graphic eq for up to 18db of solo boost in some frequencies!!! This I think should definately do the trick. Clean, lead without eq for rythm, volume on guitar rolled off...Then open up the guitar volume to make it legato friendly and footswitch the eq on to boost it to cut through!
Lastly though I don't know for sure, there is the option to put a distortion pedal to the preamps clean sound, in unity gain or slightly above in order to switch it on to play solos: Imagine a boss metalzone on the studios clean channel for solos, then off, and play heavy rythm with the lead channel set to your taste.
