Forget about a dedicated headphone amp. If you have a decent stereo amp you can use it to drive your headphones by making your own break out box or buying a "Can Opener" from Vinylflat. They go for around $65.00.
I also find that the AKG 702's are a nicely balanced headset. I prefer them over the Grado RS2's I owned for 10 years. and.....they are super comfy.
Thank me later!
I've read that the Can Opener is awesome, especially for the price. Good advice for those that already have a good component-based system. I don't have a good system, so at the advice of my two mentors, I'm building a computer-based system from the phones backwards to the 24/48 FLAC library that I've got saved and backed up on a 1tb passport drive that I can carry with me back and forth to work.
For what you would pay for a good headphone amp you can buy a good speaker based amp and add a break out box. You would most likely save money. too. There are plenty of great deals on 17-25 watt tube amps out there, that can be had. Couple that to a DA USB based pre-amp and your set. This way you have your headphone system taken care of and all you need to add is some decent speakers down the road and your (open air) playback system is up and running.
Really, I've gone your route.....with good results, too, I might add.....however, I've discovered, and learned, that there is a better way with less boxes and better sound.....that saves money. Sounds too good to be true but it is not. Unless, of course, you like lots of boxes and have a desire to stimulate our economy.
I would also add that many of the USB based AD's come with good headphone amps and usually allow for op amp rolling. Yulong and Matrix come to mind. These can easily be carried to and from work and you can use the headphone out section for pleasurable listening. I swapped out my op amps in my Matrix Mini i and have improved the headphone section. Not that the stock op amp was bad....just the new one improved it. Now I have a second headphone amp for late night listening for more than I listener.
FYI, I bought a Jolida 102....did some mods too it and use this, along with my Can Opener for daily headphone listening. I also use the Jolida to drive my Klipsch Heresey (modded of course), as a second playback system. All very nice.... and with an added sub.....works well. Not my reference system but enjoyable none the less...and affordable.
So. I paid $65 for the break out box......$300 for the amp.......$300 for the Matrix for a total of $675.....and I have a great headphone system and a good second playback system. There are other options out there....this is just one example of how you can have your cake and eat it too.
Really, don't get stuck in a paradigm!