Two things you need to know:
1.Lossless files and high bitrate mp3/ma4 files are practically indistinguishable.
I know many audiophile people swear by lossless but unless those people are 5 year old kids with pristine ear canals, then they're just imagining things.
People usually prefer to get FLAC just so they can rencode them in whatever want later. Lossless format is good for long term storing and archiving.
2.DAC's make a serious difference only if your onboard soundcard is prone to interference (most internal soundcards are) and your headphones are too high impedence to be driven without amp.
In most cases DACs make anything sound better especially if you like your music loud, doesn't matter if it's a 320kbps mp3 or FLAC.
EDIT: I didn't reply to your specific question so here it is:
Unless you've got $3000 headphones, nope. it all depends on what headphones you have. There's no need to go extreme high end with the DAC if you're not going the same way with the headphones. Headphones quality makes the most difference in audio quality.
Edited by Tad-Bravo - 6/10/14 at 3:04am