I have both headphones currently. I think that the Denon is probably the best for these. Mine probably have around 2000 hours on them...shoot who knows, maybe more. The Denon's are such a good headphone in so many ways. Really solid bass. Not a Beats By Dre type bass, but very punchy and even boomy when the song dictates. In my personal opinion, the mids are a bit recessed with vocals. I have always wondered how they are the best headphone I have ever owned when it comes to watching movies and tv, but the mids are a tad recessed with music. The soundstage is really great on the Denon's also. Wide and accurate. Also, very comfortable to wear for hours and hours and hours!
The 780 is a good. It's a MUCH brighter headphone than the Denon. I personally don't find them to be as bassy as so many people have reviewed. I really, really enjoy the Ultrasone bass, but it doesn't quite compete with the Denon. The Ultrasone always feels like it's getting ready to let the bass fly, but it seems like it's held back. Very opposite from the Edition 8. Mids are pretty solid on the 780. Fairly forward and aggressive. Soundstage is pretty good on the 780, but again, not nearly as vast as the Denon. The Ultrasone also has that surround effect. I don't really hear it on these. The voices are supposed to make you feel that voices are centered between your eyes. I think the 780 is not the best Ultrasone when it comes to this technology. The Ultrasone is also FAR LESS comfortable!