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Q5-Q6 simulate the phase inverter of the amp. As it is, I am not sure it will work, since both sides are hard-connected via the output capacitors. I'd be inclined to use a couple of mixing resistors (say, 33k for example) between the caps and the master volume. As stated above, presence will...

The way I understand it (someone correct me if I'm wrong), J177 (or BAT diodes gate-to-ground on the Series 1) are there to simulate valve cutoff and subsequent dynamic shifts. What puzzles me a bit is that some jfets already exhibit gate cutoff even at 9v, so, unsure about the need for added...

Here are a couple of examples using BJT (a tad... Old): https://www.drtube.com/schematics/marshall/2099u.gif http://www.lynx.net/~jc/SchematicMonoBlock-II.pdf For Jfets run on bipolar supplies, Gallien-Krueger amps from 1980 to late 90s feature them in several very interesting topologies :)

Replace the tonestack with the circuit on the right and you'll get roughly the same freq response, with a little extra volume on tap. Scaled down for less noise, 100k volume pot instead of 1Meg. Doesn't match 100% but reality doesn't either, due to pot tolerance ;)

FWIW the pre-dist voicing on the MT-2 is almost identical to the Ampeg VH140 (albeit using different circuits - gyrator vs. feedback loop hacks). Where the difference becomes noticeable is in the post-dist controls and voicing (big presence and resonance bumps + different tonestack). OK...

"Screamin' Diz-Buster" should be a no brainer here. Surprised it hasn't shown up on a pedal yet... Btw, long time lurker, appreciation for one of my favourite bands was a good excuse to post. Nice job on this circuit :)