I don't know if you already have researched Tom Scholz's method of overdriving the amp, but it is fairly interesting.
"His Recording Techniques, using Marshall Super Lead 100 Watt Amplifiers
Stock Marshall amps were used to record the earlier Boston records, along with his '68 Gibson Les Paul Deluxe, known as Mighty Mouse. It had in it, a Dimarzio Super Distortion Humbucking pickup, screwed down in a fixed position.
Using information provided from other musician discussion boards, Tom Scholz, used 70's Marshall Super Lead 100 watt amps, possibly a 1972 model, used as a preamp. This was achieved using a load box, to bring the signal down to line level and into a half engaged wah, used as a tone filter and other eq's, etc and into the console, direct. Using the same attenuator, he miked a standard Marshall cab, from a few feet away with an SM57 mic. This was run into a separate channel on the console and recorder. Using painstaking amounts of time and tape, to record, the sound was processed using an Eventide-910 and rack mount EQ's and other effects. Tom has said in interviews, that he will do anything in the studio to get a particular sound or groove!
Tom designed his own prototype load box, using a heat sink from an old theatrical light. After further design enhancements, it became the power soak. It received the nick name, "The Boston Strangler". It's been said, he used the blue MXR 6-Band EQ in front of the Marshall.... Only Tom could tell us this, if it is true or not, as he has been recording alone for the past 35 years.
His recordings were done at relatively low volume as compared to other musicians, using Marshall's, at the time."
In other words, he used an entire amp as a preamp, loading the power section as well and then reducing that to line level into a filter (wah) and then into a power-amp to a cabinet. I've tried to do stuff like this on the Axe, but mine don't sound anywhere nearly as good as yours do.
Good work, and hopefully this helps. By the way, Tom Scholz also used chorus quite a bit.
P.S. I want your patch!!! LOL!