my comments about HE-500 and driving them are not entirely measurement based, as in the HE-500 thread there are plenty of seasoned folks (well beyond me) recommending that to "make the HE-500 shine, get an amp that provides more than 1W." Fang may have noted this himself?
hence my initial comments about "lack of power".
You have a point in that the Concero HP may not be the absolute optimal rig for an HE-500; a lot of people will say that the HE-500 responds much better to serious power, and there are people powering their HE-500s with very, very powerful amps. However, I personally don't subscribe to the "MOAR POWER" philosophy for powering planars; the fact that planars' load impedance is almost purely resistive actually makes the math pretty simple --- most planars are not actually that difficult to drive. IIRC (and someone correct me if I'm wrong), but I think the 1W recommendation was specifically for the HE-6? My memory is hazy. The most important thing is whether or not the HP makes your HE-500 sound good to you, so I agree that it's a good idea to actually try the HE-500 with the HP personally.