Very good posts above.
I have a similar setup with the following differences: fanless, linear power supply, Paul Pang USB card, Audiophilleo, Windows Server 2012 with Audiophile Optimizer and JRiver only.
I agree with Al those are good parts. The only thing about i7 "k" processors is they dissipate a bit too much power for passive cooling, I believe, unless you drop their Hz down from the Bios. Anyway, for the setup at hand it will work perfectly well. One improvement path, though, is to get rid of rotating parts (motors), such as the fan, and then passive cooling is important. But you could overcome this by using a separate power supply to the fan.
Same thing for the music HDD, as it has a motor too. BTW, it is electrical noise you are after, not the noise you can hear by getting your ear close to the HDD.
FWIW, I connect the HDD thru SATA, but have the HDD outside the PC case, and inside a granite box. Can't tell if it makes a sonic difference, but my fanless case was rather crowded inside and it felt good to have the rotating device with the associated vibrations outside the PC case, which has no moving parts.
Powering the SSD from a battery, such as an Anker E4 has worked great for some. In my case the battery was shutting down because the power my SSD was taking was under the detection threshold for the E4 and it kept shutting down.
A linear power supply is also important. Doesn't need to be super expensive for the improvement to be audible. Mine is just a lab LPS with low ripple. A Hynes would surely be better, but this is good enough for me.
Getting the data from PC to DAC. Most of us use USB, but some prefer other options. Cerrot, who posted here, has been very vocal about his preference of SPDIF out from his Juli@ card. I have not tried it so can't comment. I would venture a general guideline would be not to use your mobo output, be it USB or SPDIF. Aftermarket cards tend to perform better, and I tend to belive powering them independently from the mobo makes a difference. Again, you can use an Anker-type battery. Jitter introduced by the power supply is an issue, and also is the clock precission. You can imagine a $100 mobo is not going to have a super clock...
And then there is the cable...I'm not saying you focus on that now, but keep it in mind for later. If you decide for USB, USB cables make a difference. And so do SPDIF (coax) cables; you'll find significant info about their length. That was a reason I chose an Audiophilleo: it's asynch USB out of the PC and doesn't require an SPDIF cable as it hooks directly to coax-in.
Having talked about all of the above, the biggest impact in sound for me was using Windows Server 2012 in core mode with Audiophile Optimizer. This was not subtle!
You could do a double boot like Al said and try WS2012 for free. Get in touch with AudioPhil, maker of the Optimizer. I think I recall he has a trial version/period or something. In any case, go to his website and download his guide and give it a careful read. He has plenty of good info besides his Optimizer.
I also run JRiver and thought about JPlay. Generally people who use a dual PC setup with JPlay say it sounds a lot better, but I didn't find that consensus on singlePC setups. Plus AudioPhil thought the incremental benefit I would get was marginal, so I decided to focus elsewhere.
It's not the time for me to get into a dual PC setup; setup is complicated enough for me now! And I have the hunch there is more to be gained from digital room correction software than from extracting more with a dual setup.
From my limited experience I would suggest the following pecking order:
1) decide on a way to get your data from PC to DAC, and execute it. This includes aftermarket card, converter (if needed), and cable. This way you will know an opaque interface is not filtering improvements upstream.
2) Try WS2012 and Optimizer
3) get a linear power supply
I believe these will yield the biggest improvement on sound.
