I spent time comparing the HE-6 to the HE-5LE using four different amplifiers.
For the HE-6, I used 1) a MacIntosh solid state amp, 2) a VTL tube amp and 3) a SimMoon Audio 3.3 SE solid state integrated amp. Each amp was 100 watts per channel.
The HE-5 LE was powered by an EF-5 amplifier.
The type of music was rock with a wide range of vocals and instrumentation.
For some reason the combination, VTL tube amp and VAC tube preamp did not bring much life to the HE-6.
The MacIntosh solid state preamp and amp sounded better with the HE-6- but still did not sound as musical as the HE-5LE /EF-5 combination.
The HE-6 and SimMoon Audio I3 SE integrated amp however had excellent synergy: full range, excellent soundstage and realistic musical detail with really powerful bass and sparkling trebel- the type of presentation that made me forget that I was evalutating equipment and just started enjoying the music. It was a far better combinaton than the HE-6 and NAD C316BEE that I had heard this Summer at the NJ meet
I found the following diferences between the HE-6 (SimMoonAudio) and HE-5 LE (EF-5):
While both Headphones had very similiar sound signatures, the HE-6 exhibited slightly more resolution and expanded sound stage. The HE-6 was more neutrally balanced
The HE-5 had slightly more emphasis in the mid and lower mid range with less detail and more centered soundstage but in a very musically pleasing way.
I can see how different people might prefer either Headphone. If you use the analogy that you can zoom into and sharpen a photograph to the point with the individual pixels overwhelm the illusion of the overall photo image, the HE-5LE does not resolve as well as the HE--6, but still achieves an excellent balance that creates a very realistic musical image.
For those listeners who want more emphasis on the mid and lower mid range, they will prefer the HE-5LE. For those who prefer, more neutrality, detailed resolution and wider soundstage, they would prefer the HE-6.
Both headphone combinations were excellent to my ears..