They don't compare. Two very different sets, K-240 Studio are very midrangey, DN-HP500 are slightly too bassy, fast, and spatious with Denon quick dynamics. K-240 lag behind in dynamics, but have more midrange/spatial detail and are circumaural. K-240 EQ is a bit weird (it's musical, but it's not really that natural). DN-HP500 EQ is more even, but they have a drop at the 3rd octave (~150-240 Hz). DN-HP500 are livelier because of quick dynamics and more present high frequencies, but they don't paint bodies of instruments as well. DN-HP500 are supra-aural, K-240 are circumaural.
Edited by Seidhepriest - 12/15/11 at 9:14am
They hardly clamp. Pretty soft on ears, softer than AH-P372.
Here's a "family photo":
AH-D1000 are most comfortable, next come DN-HP500 (they're supra-aural, but they're quite soft on ears, weight/clamp become noticeable only after some three hours or so), and AH-P372 last (these do press on ears, especially the first couple weeks).