Sounds like GAS to me, sorry! Been there so many times already during my fairly short time with synths, I can definitely relate to the feeling of ”needing” something new or even looking at something as ”that last missing piece to my otherwise perfect setup”. Maybe to get a boost of inspiration, but most commonly just out of the pure laziness of not wanting to dive deeper into the machines I already have (that’s how it is for me, not saying that’s the case with you necessarily).
Before you decide to go for either of the two, maybe get some (drum/percussion?) soundpacks for your Digitone if you feel stuck with it or feel it’s not immediate enough? Or soundpacks for your other machines, for that matter. That has been my go-to move lately if I feel GAS creeping up on me.
As people above have pointed out and you know yourself, the SubH and M:C are very different. What these two instruments would seem to have in common, however, is the immediacy, the ability to sometimes spark song ideas out of thin air. That’s how the DFAM works for me sometimes (don’t have a SubH or M:C myself). How deep these machines are in that respect is probably up to the perseverance of the user.
Even though you say the price point isn’t much of an issue, personally I’d look at it this way. Get the M:C if you want ”something new”. Also easier to find 2nd hand at the moment, if you want to go that route. Get the SubH if you want to commit. I’ve been looking at the SubH myself but feel it doesn’t add enough to my current setup at 850€.