Mark, there's no reason to believe that the Adcom is "better quality" in any aspect that would affect the sound of your system in normal operation. Within its power capabilities, which it's unlikely that you're exceeding(the amp section is of course also THX certified), the Onkyo is audibly transparent, as would be the Adcom. A longer service life might well be a possibility, but somehow changing the sound wouldn't be.

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Enjoy the music, not the equipment.