Let's be honest. JD-800 vs D-50 is more like apples and oranges. One is a classic rompler the other is VA synth (with basic sample playback).
Converters and audio processing on D-50 give a distinctive glassy character to it's samples. No other synth sounds like D-50. But then, not all people hear things the same. So it's hard to explain it to everyone, but the majority however find D-50 to have a glassy edge over its samples. This is what gives it a signature sound.
Comparing JD-800 with D-50 is somehow not a good idea, given one single patch on D-50 that can contain 4 pulse oscillators each with its own PWM. This eats the whole JD inside out, no matter which samples one uses on the JD. Further, to make things sound even thicker, each PWM-ed oscillator on D-50 can be run by its own LFO. This is really not a problem to program, because D-50 has 6 LFOs per patch.
And we didn't even touched the subject of D-50's effects processors....