George,
sampling the D50 is a real chore, because it has heavily processed sounds, with a lot a chorus and so, if you want to avoid audible artifacts, the loops have to be very long; the only exceptions are percussive sounds with short decays, like electric pianos or guitars, and the organs, which can be sampled with ultra-short loops after the very first milliseconds.
One advice: try to listen to a sound like "Staccato heaven" with all the effects off: I think that your jaw will drop, such is the difference!
I have tried to sample these sounds "dry" and then re-adding the effects (with my Ensoniq ASR 10), which has a really nice DSP. Otherwise, I had to sample everything in stereo, with 2 samples per octave and long loops starting after the first 3 seconds. It was a really memory-consuming process, but almost worked. I say almost because I couldn't completely capture the D 50 magic: maybe are those 24 bit D/A converters... However, the ASR 10 was the only sampler which went very close to the original sound: the Akai 3000 was out of question and so I think the same applies to the X1.
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Korg Kronos 61 and PA3X-Pro76, Roland G-70, BK7-m and Integra 7, Casio PX-5S, Fender Stratocaster with Fralin pickups, Fender Stratocaster with Kinman pickups, vintage Gibson SG standard.