FathomFive was part of the evolution that led to DubSub, through BassKit and all manner of related plugins. A great deal of this development had to do with taming the low frequency boost: it’s an algorithm that also does work as the head bump for ToTape, and it’s very difficult to manage.
Specifically, it delights in pumping out silly amounts of totally subsonic bass, which does nobody any good. It’s also prone to fling DC content around.
FathomFive is an incredibly simple execution of this LF boost, with a main and sub octave, a frequency voicing control, and a dry/wet. It actually sounds quite good if you don’t mind lots of energy being thrown around under ten hertz.
If you’d like a copy of FathomFive, buy a copy of DubSub and ask for FathomFive by email. I’ll send it.