George,
after reading your post I realized that I had been incorrect; when I said that the SD1 has two variations I was thinking of the "Basic" and "Advanced" ones, but then I realized that each one has two different sub-variations. So you are correct: overall, there are four variations.
Sorry for having unintentionally misled anyone.
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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.