I think stating that the DNA 500 is simply a double DNA 225 in a single chassis would be a mistake in judgment. According to what I have read, Steve McCormack has yet to devise a mod package that would add or improve on the sound of the mighty 500. There must be a reason to this. Perhaps, whatever Steve could add might simply cost $$ but not worthwhile in the sound department. If this happens to be the case, then, the 500 is an entirely different amplifier from the 225, this is not to say that the 225 is a slouch either. I own it.
Perhaps not to discount the 225, I have to say that it is the ONLY amp that I have paid almost close to retail and have not felt cheated soundwise. This means that is one hell of an amp that has plenty of merits of its own. I can only begin to phantom what the 500 is like. Can you imagine?
Paul