Require Headphone AMP and DAC advice for PC Setup with HD650

So I am brand spanking new to this site but I have been reading alot about the benefits of dedicated headphone amps and DAC's for the 650's.  (Note: I am very new to the terminology used on the site and have very little general knowledge of high end audio--but I am here to learn!)

Currently I do not own either, and I have received the HD650's as a gift and would like to find a solution to properly power these bad boys for a PC setup.

I am basically looking for some advice on a $500 dollar max budget setup to start off my audiophile adventure!  I have used a wide array of Sennheiser headphones in the past and have been working my way up the ladder.  Currently I am using the HD555's and am happy with them, however I know there is more for me out there and I would like to explore the options. 

As I mentioned before, I am looking for a headphone AMP and DAC <$500 to start.  I currently have my 555's plugged into an Asus Xonar DX 7.1 pci-e soundcard and it does the job pretty well.

I would be using this for gaming, movies, music (hip hop / electronic).  Throughout my forum browsing I have seen comments on how the 600's might be better for electronic, however that is not an option for me as I already own the 650's.  I am hoping there is other hardware available that can help remedy the aspects of the headphone that might take away from a genre like electronica.  Due to the fact that I have browsed probably thousands of posts, I cannot remember where I saw this, however I remember some people saying that some amps or DAC's can help with achieving nicer (for lack of a better term haha) treble that compliments the highs in electronic music even with the 650's allegedly being at a disadvantage for this genre.

I am also open to purchasing a headphone amp alone @ <$500 and just using the Xonar DX instead of a dedicated DAC if that is an option people think would suffice until I could afford a standalone DAC, not sure if this would be holding me back though.  Remember, my ears are virgins to high end audio and I am looking for an entry level solution -- try to remember the days when you were first starting and your expectations at that point is what im saying I guess.

Ultimately I would like to get both the Amp and Dac @ <$500, however I am looking for some guidance.

Thanks in advance. 

Also, my PC is using an Asus P8Z68 Mobo...not sure if that is relavent for my question though.

I also have a Sony STR-DN610 receiver I could use with the mix, however im pretty sure its a lower end receiver.

Links:

Sony Receiver

https://store.sony.ca/webapp/wcs/stores/servlet/ProductDisplay?catalogId=100803&storeId=20153&langId=200&productId=8198552921666232797#specifications

Asus Xonar DX 7.1 pci-e

http://www.asus.com/Multimedia/Audio_Cards/Xonar_DX/#specifications