People have torn them apart and figured it out, and you're right...it's not just EQ. But, it's not that far off.
Apparently it works like this: all-pass filter -> crossover network with gain controls on high & low bands -> unity gain summing amp -> (very low) high pass filter -> output buffer
The phase things that they talk about in the marketing are a result of the filters. But, the things they say about somehow compensating for speakers is BS. You can't tune/change anything about it except the high and low band gains. Their filter designs also wind up creating significant nulls at the crossover points (like basically all analog filters), and they wind up "smearing" over transients. That happens because the significantly nonlinear phase response of the filters ends up creating a situation where the high-frequency transient information isn't coincident with the start of the "tone" of the sound.
So....in practice it works like a 3-band boost-only active tone stack without a mid control that ends up softening transients.
It's absolutely not magic, and I've never heard them improve anything to my ears. But, people like what they like. If you like it, then you like it. Technically speaking, guitar amps are terrible amps (once we turn them up enough to "sound good"). And we all love them.
That being said...I wouldn't count on a model of it. It wouldn't be hard to do, but...and I'm trying to put this delicately....the Fractal guys seem obsessed with sound quality. People who are obsessive about sound quality generally hate Sonic Maximizers and pretty much write off BBE as a company because of how they market those things. It kind of turns into a vendetta. In full disclosure, I share this view.
Actually, BBE's marketing of these things initially made me completely write off other products like Trinnov, MiniDSP, Acourate, etc., just because the words for what those things do are superficially similar to the words that BBE uses to sell SMs. Except they're telling the truth. And what they can do is absolutely freaking amazing.....but it's a lot of work to get any of them to work right....very much different from turning a couple knobs. And pretty much the opposite effect on transients.