I have seen a Roland VA-76 for sale by owner. I have not seen a Solton X8 on the second hand market, but then, I never heard of anyone owning one either.

A big advantage of Yamaha is that people generally know what they are buying. The manuals are on-line, models are similar in many respects, and quality control is excellent. SD-1 buyers are, for the most part, purchasing on a prayer.