Frank,
I think that we can agree that the Tyros has a more "airy" but at the same time "thin" sound, due to its content of high frequencies (and a relative lack of mid-lows), while the PA1X pro and the SD1 have more "body", due to a greater content of those same mid-low frequencies.
BTW, I am not surprised that many former SD1 owners (like you and Notlos) now own a PA1X pro, because I find their overall sound very similar.
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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.