Congratulations!
Classic Preamp and I love mine! I also run the GMajor in tandem - It has 2 relays which you can use to activate 2 of the channels of the quad - HOWEVER...they are a little bit funny....for some reason they dont always change the channel when I want and you also cant get the relays to repeat the same setting across two patches...probably fixable with a firmware update somewhere along the line. I use the GMajor for the delays and reverb....and sometimes the parametric EQ for thrash tones.....works well!
Tonewise, its a good combo, does for me, but I also have a Boss GT10 which I use for effects in front of the Preamp.
I use the Quad with a 3:95 so a little different from your 2:90 but wont be far off. I also use EL34s in the outer slots of my poweramp and I think it works well, cause I can switch to all EL34s on the fly.
In terms of the preamp....I've played with this for a long time and obviously there are compromises....I set the MkIIc channel for amazing cleans (and they are!)....now that affects the MKIIc distorted tones. So I compensate by slamming it with an OD pedal and that can be overcome.
The Mk III channel I set for uber-thrash tones and dont really use the rythym part (through you can tease out some nice leads, on Ry2, again using some OD pedal).
For the heavier tones, on the normal EQ, crank the highs, keep the mids at 5 or 6, and then keep the bass fairly low. Pull all the switches. Then scoop the mids and crank the bass on the graphic EQ.
I have mine set up as follows:
Ry1: Fender clean
Ld1: Heavy Mk2c tones (boosted with OD pedal)
Ry2: Dont use
Ld2: Scooped MkIII thrash
I also use another patch for EL34 - cleans (ry1), and then I use a Crunch box into that....gives you a nice further option.
Im sure you'll enjoy it.....Ive had mine for the best part of 10 years, never really felt inclined to sell it (mmm apart from a fling I had with an Engl Savage 120)....