As mentioned before the FX-20/FX-1 use FM plus sampled sounds for the rhythm. One difference from the DX-7 is the use of multiple DACS with multiple outputs. The FX-20 has two DACS with 6 outputs each, while the FX-1 has three DACS with 6 outputs each. 12 and 18 audio channels respectively. This allows for separate instrument panning for a stereo effects, instrument doubling for chorus effects, greater headroom and less distortion. The DX-7 uses only one DAC with one output.
Secondly, the FX-20/FX-1 have analog Symphonic Chorus effects, analog 2-speed Tremolo effects, and digital reverb. Add the analog Phasor effect on the rhymic sounds, and the before mentioned big sound system, and you have a very big sound.
George
Organs
Hammond B-3/145
Hammond Super B (MIDI Controller)
Yamaha FX-1 - TM-1 x 2
Synths
Korg Triton Pro
Yamaha P-80
Native Instruments Soft Synths;
Akoustik Piano, Electrik Piano, B4II,
FM-8, Pro-53, Massive, Absynth,
OPXpro, Mtron