First off my gear is HeadRoom Micro DAC and Amp.(I don't see how people get by without the crossfeed circuit on older rock recordings) Out of the rather cheap box the high-end was brittle and harsh and the bass boomed. The midrange was just OK. I have a Ayre Acoustics system burn-in disc and after 100 hours of brown, pink, and white noise along with Zappa's G-Spot Tornado from The Yellow Shark these headphones transformed into something wonderful. The highs were tight and accurate, the bass had a lot of power, but was also accurate, and midrange vocals were something to behold. I've always been a Sennheiser/AKG man and had never listened to planars before. For $299 (plus $10 for the velour pads) I don't know if their sound is for everyone, but do yourself a favor and audition these headphones before you make your final decision. I don't think these headphones are going to be powered by iPods or most MP3 players. They are not that efficient and I don't know where the iPod friendly deal started, but if HiFiMAN did they are going to disappoint a lot of people. These are NOT appropriate for mobile use. They leak sound back in the room more than most open backed 'phones do and a dedicated headphone amp with decent gain is required to drive them. I wonder how well the Audioquest Dragonfly would drive them. I'll bet not too well. They may be efficient for planars, but they're still planars. My last pair was AKG K702s and the AKG's were quite a bit louder. I'm curious how the HE-400i's will compare. For 500 bucks they better be an improvement. I spent $150(ProCable Panorama) as I found the stock cable lacking. I know that's a lot of money for $299 headphones, but it was worth it. Plus this cable is well built and should,last for years so when I upgrade I already got the right cable. If I get an amp with 1/4in. jacks, I'll have to send it back to cablePro for a new plug.
 
I know there are better sounding amps out there than the HeadRoom Micro, but none that have a crossfeed circuit. Maybe HeadRoom will start building amps again someday. I just sent it in to replace all the 3.5mm jacks. Getting it back today! Been using the headphone jack on a pair of powered computer speakers with the volume 3/4 of the way up and with the bars on the graphic eq on Foobar maxed out to get more gain. There's just no way any player is gonna be hot enough for these..