The high and mid of HE-500 continues to improve as more hours has been put on.
I have also tried the pleather pads and definitely not my choice since it increases the reflection and cause "confined" sound. So I quickly switched back to velour pads.
And tonight I pulled out my Rotel integrated amp RA-970BX so that I can amp both HE-500 and HE-6. I can only compare the high and mid freq since Rotel is not a Pass Lab.
And I can clearly hear the advantage of HE-6 in the high/mid. It just has much nicer harmonic and sonic resolution. Using spectroscopy as an example, the HE-500 has lower resolution so that nearby freq components were smeared together. However, HE-6 provide richer variation in tonality and texture among different frequencies which was certainly more interesting and pleasing to the ear.
Still, I can happily live with HE-500 considering its much lower cost for relaxed listening session.