Check out this site AudioScienceReview for actual objective measurement of DAC's, headphone amps and now even speakers. The main contributor, amirm, uses hi-resolution test gear, often with brutal results for high priced boutique brands. Reading through the other posts here, several of the suggestions tested very well on AudioScienceReview and would be good choices.
It's a fascinating website, isn't it? Tons of great objective info. Hope it's for real - appears to be. From memory, I don't think the reviewed Chord products measured well yet magazines and enthusiasts rave over them.