Wow. I tried them both at local audio store (side by side) and D5k were the run away winner by my ears. Amp may not have been up to driving 650's, not sure. The Denons were clearly more comfortable on my large head.

Comfort is a non-issue with the 650 as they change considerably over the first few weeks. As for sound quality, I at least would like to hear why the D5000 was a "runaway winner."

Several criteria play into that assesment. The biggest one:  From the amp that was driving all the phones, The Denons had a the clearest, fullest and most deeply joyful sound I've ever heard.

This was aginst some other Denons, some Grados and the one Sennheiser.

It is possible that the amp might not been up to whatever it needed to be to make the Senn's sound right.

Mostly I was comparinig at similar volumes though I could adjust it up and down however I liked. But from what I heard, the 650's were flat and distant in comparison.

I liked the D5K's better than the D7K's. So maybe it's just something with the sound I like. Also, I could not say how long anything was burned in for.

So nothing real technical for me, just a clear sound preferance.