Looking for some input from Theorem owners.   I'm currently look for a portable Amp/DAC that pairs well with my iPod touch, and many of the features of the Theorem appeal to me, such as the battery life and being able to charge my iPod while listening. The two headphones I currently own are...

I am looking for recommendations for a portable Amp/DAC combo that works well paired up with PSB M4U 1 headphones. As far as price goes, I would like to keep it around $300 at most, but wouldn't mind spending more to get something that is worth it. What would some of you recommend?