Bass integration problems? It seems like it could be as simple as the MM7’s are simply damped plenty to start, so that while too much feedback would be sterile, they probably need a bit more than many tube amps provide, and more power. The 11” Accutons are pretty well damped, with underhung VC, so they are actually electrically very similar to most high sensitivity drivers found in horns, single driver, vintage, etc. but you put that into a box with treatment and it will be damped enough that power will be trying harder to “get there” than it will be to stop/correct going too far. The sub towers really work on the low stuff, they are probably a lot harder to differentiate except that not all transformers can produce signal so low.