Put a little over 1 watt per channel into the HE-500, and it will work, to keep it simple. The HE-500 loves current. Feed it all day. Orthos in general. However, to keep it simple, when looking at amps, simply look to see how much it can output at 38ohms and make sure it's about 1 watt or more. Ideally more to have overhead.
Asgard puts about 1 watt into 38ohms.
Lyr puts a little over 5 watts into 38ohms.
NFB12 puts a little over 2 watts into 38ohms.
Countless AV receivers can output unknown amount of power into 38ohms; I've tested 4 and all 4 can drive my HE500 quite well.
They drive the HE500 great. I preferred the sound of the Lyr/NFB over the Asgard. I can't say for sure if it's the power difference or simply signature/preference though.
Point is, you don't have to spend big to make the HE-500 sing.
what kind of headphone stand is that? with those screwed on feets? it looks nice! simple and classy!