After trying a Duncan pickup booster pedal in front of an OTS 100, I thought i`d try it in the loop.
The results are worth mentioning as a strat & tele can be made to sound alot fuller in tone.
The frequency filters on this pedal are the key to achieving this.. and there are 3 positions.
* middle position is standard with no frequency shift, but you can boost the signal if you wish via a gain pot.
*Top position is standard PAF type humbucker
*Bottom position is hot humbucker.

Using single coil fender pickups with the frequency filter on hot humbucker, and gain pot at minimum on the pedal, it`s possible to achieve a very warm  tone very similar to a PAF type humbucker.
It pays to run the master vol higher on the amp, while keeping the volume level on the amp a bit lower than you usually would.
This compensates for keeping things balanced from my experience.

There seems to be a few strat players that aren`t totally happy with the sonic results of this type guitar in the OTS.
From my experience, if you use single coil pickups and would like a warmer,fatter tone that is balanced in the frequencies, give this booster pedal a try.

Hi there... You`re probably right about the twin tube acting as a tube buffer in the loop.
Have you tried the TT in the loop with a strat plugged in the amp..?
Indeed the Duncan PB in the loop has very good results for fattening up a stratocaster.
I get an authentic, warm jazz tone using the front pickup with the tone pot rolled back to around 6/7
And there`s no muddy or dull tone.. just warm, fat and plenty of balanced clarity.. sounding very PAFish.

Turning the strat tone pot to 10, you have a fat strat tone... and without any loss of the typical strat character.
Which is, IMHO.. quite an improvment over the usual strat sound.
To compare against the normal strat tone, all you have to do is flick the frequency filter back in the middle position.

The top postion on the frequency filter is very usable as well to fatten the tone, but with a little less 'fat' than the bottom position.

Cheers