Yes, the DGX 505 is the newer of the models. My understanding is that Yammie will be replacing the DGX 505 soon. I believe someone mentioned that the replacments were at winter NAMM.

I owned a DGX 505, not a bad instrument at all. I traded it for a Casio Privia 400 because I wanted a more acoustic type piano action. It came down to personal preference. For home I have a Clavinova CVP 307, in my opinion it's one of the best products avaliable. Everything from the action to the piano samples, styles and a lot other features. IMHO the pianos are so good that I sold my Samick grand piano to get the Clavinova. No need for frequent tunings, regulation and other work that acoustic pianos need to be kept in good shape.