As far as I can tell, on the original Stage, the EX version really was just a cosmetic update with doubled storage for pianos.
For the Stage 2 the changes between the regular and EX models were a bit more extensive.
analogika wrote:The Stage 2 EX Compact also shifted the keyboard to start at low E (Rhodes standard) instead of the F.
The 2EX also changed the power cable (for the better, IEC instead of that flimsy figure-8 cable) and the knobs (for the worse, plastic shafts intead of metal).
The 76-key version moved from the HA to HP keybed (much better for portability, but worse for playing feel).
Also, the knobs for the EQ and synth section gained a center detent.
Small changes for sure, and nothing involving the sound engines, but anyway it was a bit more than "just twice the piano memory".