Ok,
for me a pro/serious FM synth is a synth that allows you to edit all the FM parameters in a deep way, without limitations and also by giving you some new features regarding the FM never seen before.
For that reason I’ve mentioned the Yamaha FM-X synthesis, because this kind of synthesis seems to me to be near to a new FM idea.
I don’t know how much “deep” are the Digitone FM capabilities (I don’t care about the polyphony and the number of 4 Operators, they are enough)…
Yamaha MODX is more expensive and It has non-FM features that I don’t want like the AWM2 or the VA emulation, I’de prefer to buy a Korg Minilogue for analog sounds
but I see that It has a great Matrix page to modulate parameters, Macros to manage more layers at the same time and better FXs maybe
Said that, I guess that the Digitone is very funny and fast to use, great for a live use
I’m an electronic/ambient musician and I don’t use so much FM piano or other Marimba FM sounds, so I hope that Digitone opens to other new FM sounds
I have the FM8 and the Yamaha TX802 and I love them, I love the Fm synthesis
Maybe a Digitone + Reface DX could be a good solution, even if I have my doubts about the Reface because it would be just a duplicate (or less) of the Digitone without anything of different