Well, this is to MY ears... and (as some people sometimes criticise) if you look at my signature beneath this post, I do have both pairs...
The HD580s are more than likely the more accurate of the two pairs, but they don't sound like it when you do a direct A/B comparison... the HD580s sound quite bassy, no midrange to speak of and a sparkling (potentially bright) treble
Whereas the CD1700s sound about level, if not ever so slightly bassier - to my ears the bass is of a slightly more refined character (probably due to the closed nature of the CD1700 housings)... the mids, these are sumptuous, cuddly you could say ~ pretty ideal for vocals and instruments, but can sound syrupy if partnered with a wrong component (hence why I sold my original pair last year), and the treble? - I wouldn't really say rolled off, more - polite, there is less sibilance to my ears than the HD580s, but maybe it could do with slightly more sparkle to generate that last little ouce of excitement.
Not really appropriate to the context of your thread, but it may help you decide if you look at other reviews... I find that the HD580 is at one end of an (admittedly small) scale sonically, with the CD1700s at the other, and the ETY ER4Ps right in the middle - hitting the sweet spot, so - its really a case of picking your poison
I hope its of help?!