Free FM Synthesizer Dexed (VST Windows and Mac) – Page 139 – Instruments Forum

Every 4-operator sine-only algorithm (DX21/DX27/DX100/FB-01) is a mathematical subset of 6-operator FM. They can be replicated with 100% accuracy on a DX7 or Dexed by mapping the 4-op algorithm to its 6-op equivalent and disabling the two extra operators by setting their output levels to 0.

The only challenge is that parameter scaling (envelopes and output levels) differs between the hardware architectures, and you cannot convert TX81Z or DX11 patches that use the non-sine operator waveforms, as the original DX7 is strictly sine-only.