Starter Dac for Headphones...


i've done a bit of research on the net but since there looks to be a lot of market i'm a bit overwhelmed on the different opinions/needs,etc...
In your opinion, what are the best features that i need to look about dac for headphones? usb-powered is good enough? Digital/analog volume control makes a big difference?
I don't need a portable one, i mostly listen to my music on my computer and i found "portable" dac a bit ridiculous lolll. Anyway, which one would consider in my case if i have a budget at around 400, 500 max? Would you suggest me to try them out first, because i don't know if the type of music would change the choices i have... (i listen to trance music, house, trip-hop, downtempo, jazz, etc)
I thank you in advance for your advices it means a lot :)
freb03
I directed questions to the one that told me something but you can reply too :)

To Nonoise

If i find a used DACmini of Centrance i'll jump on it :p
But for the in-line dac i guess i'll need an amp? Do you know if this will be good with the Valhalla amp from Schiit? I heard that tube amp are really good (for warmness sound ;) )
How do you compare the inline DAC from Centrance to the one from Schiit?

To Mateored

I take note about a schiit stack :)

To Jedinite24

The problem is that it's hard to know the difference between the AKG Q701 and the Beats pro because in the end, i will have a different dac... so it change all the frequency balance. And i'm not sure if there's a store that woud let me try all the options :(
I use the Audioengine D1 USB DAC/headphone amp to listen to music on my computer. It sounds very good and it's not expensive. A nice item for the budding a'phile.