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Basically they have introduced a new digital piano, a general midi module, an USB/SD card reader for the old arrangers like the SD1 and, again, the Midjay Pro (already introduced the last year).

I think its great that Ketron still do stuff for older models. The SD1 is pretty ancient now but still widely used and an excellent keyboard and the X1/X4 are also still very popular. If I had one I would definately go for this upgrade. The ability to be able to use SSD (sd card) and play back wav and mp3 files is very usefull, as well as connectivity with external devices.