Re: How many V20 users have over the ear "high impedence"??
The AKG K712s are my favorite. The have a clarity and spaciousness that I love and a tight accurate bottom end w/out being boomy. They're also extremely comfortable. The Q701s are the same just with slightly less bass impact. The Senn HD650s don't sound very engaging to me being driven by the V10 or V20. I usually listen to them with a cheap $100 Chinese balanced cable connected to my OPPO HA-1. There, they sound better than I'd ever heard them sound before with a pricey unbalanced Cardas cable connected to my Burson HA-160D. A balanced connection really makes a difference for some headphones.
My favorite headphones for the V10 and V20 are, believe it or not, my Bose QC25s. The bass sounds just right and there's a nice helping of that clarity I'm so fond of. They're very easy to drive being low impedance but they sound good.