Eric,
The Ketron distributor in the USA says prices will be known on or around July 1. Other differences will be no 16 track sequencer and no sampler in the XD3 as there is in the X4. The sequencer in the XD3 is a one track direct to disk sequencer. This is like the sequencer in the MS40 module from several years ago.
In the information Dnj posted I don't see anything about registration memories. I would be surprised if this wasn't included because every Solton/Ketron product has registration memories. Maybe AJ can answer this.
George Kaye
Kaye's Music Scene
Reseda, California