Re: "Low gain" Marshall style pedal options?
The following is my opinion, and that said, of course there may be disagreements with it.
There is a huge difference between the results (with valve amps ... just a reminder) obtained at low volumes and at high volumes. At low volumes, when the power tubes don't do their saturation thing, them amp in a box kinda pedals may sound great. I've been into them some time ago. Yet, at high volumes, the real tone of the amp (filter caps, power tubes, speaker) starts to dominate, in my opinion. And many of the amp in a box pedals, start sounding not that much different. Their differences at high volumes, to me, are primarily to be found in the resulting compression, softness/responsiveness of bass (then again I am keeping all them aspects about pickups and their mags fixed), and eq. So two amp in a box pedals that sound great and different at low volumes, I have experienced, sound quite similar at high volumes.
Timmy, from what I understand, is built knowing all of this. PaulC is hell of a guy, he has a Tweed 5E3 mod (Ampeg mod) which is accepted by many of them amp maniacs... Just search for it in Metro forum or Amp Garage. That pedal is sorta clean to medium gain boost with bass and treble. So itself is not a big thing, but when it comes working with the amp at high volumes... Well that's where the gold mine is. It is not expensive, that's the other thing... A bit hard to come by, due to the demand side... Anyways, it lacks compression, you gotta get it from the amp. If you wanna have a bit compression Xotic BB Andy Timmons is good actually.
TC's spark (the big version) is also very cool in that regard. Again, not much compression.
Then, there is also Lovepedal's OD11, a bit more TS type of sound but still good. Very similar to Timmy. For a while there was a quarrel with PaulC and Sean, because OD11 seems to be "extensively" inspired by the very Timmy design... Then them TGP admins took that thread somewhere where it is not observable to the public.
So, my humble opinion is that... You have a Princeton Reverb. Very good amp! 6V6's... Very cool. And if you can use it at high volumes, Timmy (or a close alternative) would be able to help you "shape" the whole combination a bit more Marshall sounding. At low volumes, that pedal sounds good as well... It's gain is very useable at lows too... I am powering mine at 18V to get more harmonics and all...
BTW Giggity is cool as well, at high volumes too... It can do all this, and also do "unboost"... make your amp clean. It is not advertised like this, but I think that's a mistake. The "unboost" thing is exactly what made me an addict. I am using a 5E3 clone with HBs... And the amp has all the gain, love it. But not that suitable for rythm work. So the Giggity is washing off the gain, adding sparkle and air... Anyway, that's not the subject.
Hope this helps and you find what you are looking for.
B