Headphones

I use a Cambridge audio DAC from my apple OS to my Linn Klassic receiver and KEF Q35 speakers. Using Songbird to handle flac files , Internet radio  and Berlin Phil Digital Concert Hall I find the sound very good. Two things:

1) I am looking for Headphones £300ish that will deliver optimum orchestral sound but am unaware of any specifically designed for orchestral music.

2) If I replaced my DAC with something like the Cambridge Audio Sonata NP30 reviewed by Andrew Everard in Oct Gramaphone would it improve the sound I get?