The piano sound isn't particularly good, I think it's the same bright pop-like CF3 sample as the Motif XS piano.
The D deck was already released around 2004, I think.

Edit: As I said in a post above, the DDK-7 is available only for Asia, where it still seems to be a current model. I don't know to what extent the sounds have been updated since the version released 10 years ago.
I read that a German pipe organ distributor also distributed the Stagea a few years ago in a sort of cooperation with Yamaha. Yamaha itself sees no market for it outside of Asia.