DX7 type synth keys with velocity and aftertouch. Uncountable permutations of sounds. Ability to layer three manuals. Two octave bass pedals. Fm synthesis Rom sounds with little tweaking possibility. Programmable LFO, two octace bass pedals, drawbar organ with some unusual footage options.
Huge tone cabinets, top quality.
Sustain lever, pedal control for pitch down or start stop functions. Non programmable arpeggiators, drum section. But patterns can be sequenced to create a full rhytm track for a song.
Audio input (but does not benefit from the internal effects.
Basic digital reverb, leslie simulation, chorus and ensemble.
10 channel audio output.
Gets some time to get familiar with the instrument with so many buttons. But the architecture is pretty straightforward.
It uses an early FM synth engine. Not much like the DX series but somewhat similar.
Some patches are amazingly realistic but with todays standards I call the FX1 sounds characteristic rather than realistic.
The whole construction that embraces you is very inspiring. I am glad to have one and will not apart ever.