There is a technical reason that the Sub 37 can’t do that osc FM that you’re talking about.
I’m just going from memory, but basically, because the Sub 37’s osc can be modulated from many different sources it’s fed by a digital control, so they couldn’t have the osc do analogue modulation.
Osc 1 and Osc 2 pitches can both be set as modulation sources though… so it’s not “real” FM but at least there is some sort of work around.
Just a trade off from the design… but considering the Sub 37’s extensive modulation options. It’s a trade i’m happy with.
Voyager can (obviously) do true FM and i’m pretty sure the Little/Slim Phattys can also do this… but I don’t actualhave either a L/SPhatty or a Voyager so don’t quote me on that 