If you have turn the volume up to max just to get to acceptable listening volumes, that is a sign that you need some kind of amp. I'd recommend a CMOY amp, because I used one with an AKG Q701 and it had plenty of power. This was the JDS Labs CMOY version -- make sure to read reviews if you buy a different version, as there are many variations.
Fiio amps are also quite popular.
wait is he only using a Dac...
as a rule try not to buy a dac without an amp, there are many nice combo units, but just make sure your feeding your dac into some kind of dedicated amp
and the cMoy is a good option, the Fiio E11 is too