OP: As an owner of a Luxman 507ux, and an admirer of D'Agostino I've been thinking about your dilemma.
Honestly I find the Luxman and D'Agostino to be VERY similar. So much so that it seems a shame to make that move, in either direction.
I think if you really want "more and better" sounding you should instead consider going to the Luxman separates OR perhaps an Ayre. I recommend the Ayre not becuase I actually think it's better but because it's significantly different sounding. I recommend the separates because the additional current in the top end amps can really make a difference.