If you're still reading this anyway, be sure to let us know your wa6se impressions with the he-500 if you do pick a pair up. There's not really a ton of information around on how the woo amps pair. Only a few opinions. Most people just seem to get a Lyr which I'm sure is fine, but I like the woo stuff quite a bit more so I'd like to know more about it :) I'd personally go for a woo any day over the lyr. I just get a weird feeling that the lyr would not suit me. Also I guess I'm afraid that it's over hyped. I'm sure it is fine though.
I've tried two Darkvoice amps with my HE-500's and they could not drive them. I have pretty much given up on OTL amps for these headphones. Even if they can play loud enough the dampening factor is a disaster (they completely lose it in the low frequency). I went solid state for these HP's and they are very happy. I still love tubes but they are not the answer for the HE-500. Some like the Lyr just use the tubes in the circuit to introduce tube harmonics but they are really solid state/hybrid amps which is why they can control ortho's. I used to do that in some of the gear I manufactured back in the 80's and 90's and it can work well. Frankly, I don't think the HE-500 needs tubes to be very musical.