I've owned the HE-500, HE-400i, MD-4XX, HE-5LE, HE5SE, HE6SE - and heard the HE-6, Sundara, 400s, and the 560 - pretty much all the round form HFM cans of the past 11 years.
For my money, the HE-500 nestles in #2 after the HE-6, and ahead of the HE6SE (Adorama - read about my issues) and 560 (v1) - the next two best.
The HE-500 is amazing in how much a mid centric can it is - and yet the bass and treble are both obviously excellent in their own way. It needs 2 wpc at 50 ohms to get the best out of it.
It along with the HE-6 are among the most modded cans of all time - not because the driver stinks, but because it is superb, but the stock cable, headband, rear screen, and pads are all haphazard/low quality.
I've got the HE6SE, HEX v2, HD-600 also and the 500 is still getting 50-70% of my listening.
The 560 is clean, has a bit of bite around 9 kHz, quite nice, just not a 500. Let's try this way if the he-6 is a 97/100, the 500 is a 94/100 and the 560 is an 88/100 and an unmodified 4XX is a 78/100. The 500 and 6 with mods are a lot closer to real music than other round form HFM no matter what u do to them. The Arya is better outside bass impact then the 6. But even used - Arya (~1100) and HE-6 (~900) cost a lot. The 500 is less than half that (~400).