[Aastii]

I am looking at picking up a set of HD 650's to be used mainly with my PC, however upon reading up feel that am amp may be in order too (and potentially a sound card).
 
At the moment I have an Asus Xonar D2X, with a pair of CAL!2's plugged straight into it. I am in the UK, so if I had a £4000 budget for the lot, the headphones will take around £220 from the budget, leaving me with £180. My question then is twofold:
 
1. Would it be worth upgrading my sound card too? The only real upgrade would be going to an Asus Xonar Essence STX / STX II, which I am not sure would be a great leap to be honest.
2. What would be a decent amp to pair with them?

 

[PurpleAngel]

  I am looking at picking up a set of HD 650's to be used mainly with my PC, however upon reading up feel that am amp may be in order too (and potentially a sound card).
 
At the moment I have an Asus Xonar D2X, with a pair of CAL!2's plugged straight into it. I am in the UK, so if I had a £4000 budget for the lot, the headphones will take around £220 from the budget, leaving me with £180. My question then is twofold:
 
1. Would it be worth upgrading my sound card too? The only real upgrade would be going to an Asus Xonar Essence STX / STX II, which I am not sure would be a great leap to be honest.
2. What would be a decent amp to pair with them?

 
The Essence STX and D2X use a lot of the same parts, like same series of PCM17XX DAC chips.
Exactly the same op-amps (JRC2114) and audio processor (C-Media CMI8788).
So the STX is basically the D2X, but with a dedicated headphone amplifier installed.
(the D2X supports 7.1 analog out for speakers, the STX only 2.0, but I'm guessing that does not matter)
So swapping out the D2X, for the STX, would not be worth it.
Better to just buy an external headphone amplifier and connect it to the D2X's Front Speaker/Headphone jack.
 
An O2 (Objective 2) headphone amplifier would make a decent budget amplifier, to drive the Sennheiser HD650 headphones.
The Epiphany Acoustics EHP-O2 (O2 amp) use to sell in the UK for 77 GBP, might find a used one around.
The O2 is at least a slightly better headphone amplifier, then the one built into the STX.
 
Maybe a (85 GBP?) Bravo Audio tube headphone amplifier?
 
You might read up and ask on this thread about amplifiers for driving the 300-Ohm HD650.
http://www.head-fi.org/t/197776/sennheiser-hd650-impressions-thread
 
Hopefully you disabled the motherboard's on-board audio, in the BIOS, when you installed the D2X.
Have you tried these third party drivers, the Unified Xonar Drivers?
http://maxedtech.com/asus-xonar-unified-drivers/

 

[Aastii]

Thanks, any reason for such a cheap amp considering my budget?
 
With regards to the audio + drivers, no onboard is not disabled but I have had no issues with conflicts, and yes I have the third party drivers installed, it is essential for Windows 10 since Asus haven't released fully working drivers, so otherwise the number of options in the Xonar Audio Centre is basically zero!

 

[k4rstar]

With a budget of 180GBP you can either go tube or solid state, do a little research to see which option you think you would prefer. If you do go solid state I would recommend either the O2 offering from JDS Labs or the Aune X1S.
 
Either way I would bypass the sound card in favor of the USB out from the DACs in either of those amps.

 

[PurpleAngel]

  Thanks, any reason for such a cheap amp considering my budget?
 
With regards to the audio + drivers, no on-board is not disabled but I have had no issues with conflicts, and yes I have the third party drivers installed, it is essential for Windows 10 since Asus haven't released fully working drivers, so otherwise the number of options in the Xonar Audio Centre is basically zero!

 
Just trying to point out the best bang for the buck options.
Some people may think they have to spend more for an amplifier then they really have to.
For a fixed budget, the less you spend for the headphone amplifier, the more you can spend for headphones.
So just trying to point out reasonable options, before you make the final decision.
 
With 300-Ohm Sennheiser HD650, guess you really want to spend the most you can, for the amplifier, to bring out the best in the HD650.
 
I like disabling on-board audio, in the BIOS, as there is a small chance that active on-board, will have a negative effect, with an add-on internal sound card.