I'm using both at this very moment, and I wouldn't say that the HD800 is a much, much better headphone. Yes, the HD800 is unphased by the HE-500 with it's detail extraction, soundstage and imaging capabilities, and it's unforgiving ability to show the tiniest nuances of a recording. But I find that the HE-500 beats out the HD800 when it comes to naturalness, a slightly sweeter midrange, and non tizzy highs. The HD800 is a better headphone when it comes to technicalaties, but it's two totally different flavors.
Also, I think the HD800 is slightly overpriced at $1,499, and the HE-500 is a absolutely sonic baragin at $699, as it's a part of Summit-Fi. If I could price them, the HD800 would be about $1099, and the HE-500, at the original price of $899.
Edited by Austin Morrow - 12/21/13 at 12:35pm