The 5LE treble / mids balance is off? More like more nutral than what you may be used to with the 500s. The 500s are the one that has off treble and a slight mid range hump.
The He 500 are certainly more laid back than anything I've ever tried; mainly due to the dip at mid treble (at around 5-6k), however they aren't dark sounding due to their peak at 10k. Looking at the charts I can see why the He-5le's don't lack aggressiveness and detail; from the graphs you can see the He-5le's have a more caved in mid range (at 2k) and more accentuated mid treble (4-6k). The incline may cause vocals to sound more clear and upfront; 5k has the quality of bringing everything more forward (the He-500's on the hand recesses these frequencies a quite a bit more than the He-5le's). The more detail you may be hearing in the He-5le's are due to the hump at 7k (the He-500 recesses the 7-10k just a bit more, but still has sparkling treble qualities). The He-500's are pretty easy to figure out (unlike my Fostex T50rp's- the mids on this thing are a complete enigma, but are absolutely wonderful), the're just lazy headphones (best way I can describe them). But from my guess, they're actually more neutral sounding than the He-5le's.
Edit: graphs are in next post
^You are on the right track
If I am not mistaken (which I might be) it seems to me that the 5le has some kind of resonance in the treble, sometimes rendering cymbals and the like slightly unnatural.
Tyll at innerfedelity calls it tizzy sounding, most likely due to an overall increase in treble energy compared to the He-500's. I don't really believe what most people say about the He series anymore; supposedly He-6 is master class, He-5le is pretty good too, the He-5's are the black sheep, the He-4 the pure, angellic version of the He-500, and the He-500's? Well they're kind of heavy.
Does anyone know how the La Figaro 339 pairs with the HE-500 compared to the Emotiva? Is the 339 even enough to power the HE-500? I realize that there very well may have been a comparison on this thread but I don't really have the patience to go through the 766 pages that is this thread.
The He-500 is a headphone without faults, better yet, it does everything well and somethings amazingly. But its lack of aggressiveness can make you forget that you're listening to music. I sometimes find myself wondering why my neck hurts and then I remember I had my He-500's on. I find myself skipping through entire songs unaware of its presence.