I have heard both of them.
For me, the AVR 8500 is the better performing unit.
The Denon is a fine machine & capable of some quality stuff.
However, the Harmon is a better performer in 2 channel mode.
To my ears, it held it's nerve a little better than the Denon did @ reference levels.
That's not to say the Denon didn't do the business, as it was very good on the Saving Private Ryan disc which was running.
Seems as though the Harmon designers were happy with fitting 5 high current amps into the 8500, instead of the 7 in the A1SR.
You cant really go wrong with either actually, although, it may come down to the fact that you may need a 7 channel system (and you dont want to buy an extra 2 channel amp for the 8500)
Not everybody likes the Harmon styling.
I went for the 8500 as it was just that little bit better @ doing the whole package, and, at the time, i got a pretty good price on it.
Adz