One day I encountered the quirky OuiLead, a Japanese synth that has some fantastic sounds, but sadly no patch editing. Definitely worth grabbing, especially as it is free and regularly updated.
Some odd sound toys appeared that let you play with a single FM sound, varying the frequencies etc for some unusual effects, but they weren't really what I was looking for.
The makers of the fabulous Digidrummer have created Destiny, an FM synth, but it looks a tad basic for me.
Then came Pianofly, a truly brilliant little 3-op FM synth with extensive editing and a great user interface. I'm getting closer to my TX81z replacement.
Finally this morning I came across Innocencer, which I wasn't sure what to make of - it looks a bit like OuiLead and was free, so I thought I'd give it a go. It turns out it's a 4-op FM synth with control over the algorithms. The closest yet to my TX81z dream! I haven't tried out its
innovative midi file playback yet, but it does a great job as a polyphonic FM synth. Clearly this is a developer with the potential to make what I seek. And I'd pay a good price for a proper emulator that could load up my gazillions of SYSEX formatted TX81z (and other Yamaha FM synth) patches.
So far so happy.