Thats the problem I'm facing, I have the money for the HE500's and want to get them really bad however my parents won't let me spend my money on them, let alone amp/dac combo for 500$+. Luckily I already have a large amp/dac at home that will power any headphones sub1000$ without any issues, I wouldn't be able to imagine how I would be possibly able to convince my parents to spend money on a headphone amp.
You could get the HD400 and run a lot more amps comfortably. My DAP runs all my headphones o.k., so a nice DAP may be an option, at least. Have you checked out the W4S uDacHD. It's new and i think it may handle orthos, but you could call them and ask them for sure. It's so small, nobody would ask how much you paid for it.