I played an SD1 plus today; basically is the same keyboard, with the new sounds and styles from OS 4.0 (but without the reload option if you don't like them). The new piano sound is intended for rock music (it's kind of bright) and can be loaded from the hard disk. I am 100% sure that the new sounds and styles will be made available through one of the Ketron groups found on Yahoo.
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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.