As I've indicated in my previous posts on the HE-5LE, I thought that the signature was just ever so slightly better than the HE-500. Possibly, a small bit of refinement improvement. The upper mids on the HE-500 appear to have a slight advantage, if that is one seeks. However, I have repeatedly played various passages of tracks in music where I knew how certain frequencies would respond. With regards to bass and sub-bass "oomph" the HE-5LE easily matched those of the HE-500 in same level, depth and quality. The HE-5LE has a special "top end" to the signature. This is a bit more apparent in various uses of percussion. It's not a sharp "sizzle", but a nice, refined presence that screams "audiophile bargain" for the prices the HE-5LE typically sell at.
The $599 HE-5LE from Moon-Audio, if they have stock, should not be overlooked. Easily, that is an excellent bargain in this hobby ... even when compared to the "B" stock HE-500 @ $559 - $629 or so from Headphone.com when they have those items listed.
The additional power that the HE-5LE needs over the HE-500, is very small, and should not be considered a deal breaker by any means for those who are looking to purchase.