I currently have the 840a, and am demoing a McIntosh 6500 right now. They both have a distinctly different sound, but I can't really decide which I like better. I would assume the Mc would have a much more accurate sound considering their price and their reputation. I don't know though, the treble just seems better to me on my 840, maybe I'm just used to it's sound since I've had it for so long. So far I haven't been able to justify getting the 6500 yet.
I think you are experiencing yout first brush with the McIntosh house sound. Some, like myself, are big fans. To others, it may be an acquired taste or may never sound right. Your ears will let you know soon enough.