The great thing about FM is that it is quite a digital technology ..

Dexed:

https://zynthian.org/engines/_engine-list/engine-dexed

.. can be run on Zynthian (http://zynthian.com/)

And, there is the Monome, which supports various amazing FM thingies too:

https://llllllll.co/t/triggers-sorens-standalone-fm-synth/50...

https://llllllll.co/t/xd1-is-an-fm-synth/59150

Seriously the TX81Z is at the root of a lot of inspiring synth engines that have appeared since... and in the case of the Monome/Zynthian examples, proves yet again that no matter how complicated the synth engine behind it, as long as you've got a semi-decent user interface, people will cope and make tunes.

Which is why the TX81Z is such an oddity! :)

(Disclaimer: FS1R owner)