cel4145
Headphoneus Supremus
But as Bobby S said earlier, buying an AMP now kind of "locks" me within a specific range of headphones that is "usable" with the AMP.
A lot of people on head-fi would not agree with Bobby S.
The EHP-O2D will work well with 99% of the headphones out there, and the few that it won't be a great choice, are way above your current spending budget. You'd have to get well into this audio hobby to a point where you wouldn't mind buying another headphone amp/dac.
Even the E17 is going to work well with 99% of the headphones in the under $300 range. The EHP-O2D is the dac/headphone amp to get in your current budget range for something that is easily transportable. You'll find many head-fiers who feel satisfied using it with big headphone collections.
I have the ODAC paired with a different headphone amp. I seen no reason to ever upgrade my ODAC. I used to have the Objective 2. I upgraded to get a headphone amp with a pre-amp for speakers. But otherwise, I don't know that there was much benefit in me upgrading.
Read the reviews for the O2: http://www.head-fi.org/products/jds-labs-assembled-objective2-headphone-amplifier/reviews
Then ask questions in the O2/ODAC thread:
http://www.head-fi.org/t/616331/o2-amp-odac
Now if you ever get to the stage that some people do of trying to find "the" perfect amp to pair with your favorite headphones, that's another thing entirely. But you are long way from that stage, and a lot of budget away. LOL