1) Virtual surround:
I have CMSS 3D, and when I looked up that versus Dolby's solution most of the comments I saw suggested CMSS 3D was better.
*I didn't know how to use it properly. It's a bit confusing:
a) CMSS 3D on
b) Playback Devices to 5.1
c) profile to HEADPHONES in other software
Then, go back and verify playback devices is not only still 5.1 (using your headphones) but that the TEST audio works with nothing muted.
**I'm not certain the above applies to you however, as you may have different SOFTWARE that makes this easier. Just make sure you have the proper software installed and look for any Virtual Surround option if different from the above.
2) Sound card?
I'm not sure you'd see much difference, nor can I test. I do notice a big difference between my Auzentech X-Fi Forte (not available now) and my Z77 Sabertooth (ALC892 I believe). Auzentech also gave me their best OP-AMP upgrade as well so I could test for them.
I have excellent quality speakers (M-Audio AV40) and great Sony headphones (MDR-V700). My headphones should be very comparable to yours.
However, your onboard audio is better than mine by likely four generations (ALC1150 ?). The Realtek chip is slightly newer, and more importantly you have an EMI shield and two OP-AMPS (one for front panel). The OP-AMP makes a huge difference as it helps prevent distortion in the analog signal.
So to be clear, you have a better Realtek chip (digital data) which then is amplified by better OP-AMPS then I have.
3) DAC?
A good DAC is likely better than most sound cards I've seen, however again your onboard sound is about as good as onboard gets and possibly to the point where it's hard to tell the difference between it and something a lot "better".
I've looked for good reviews for a long time, and have discovered the only way is to test yourself. Some say "no difference" now but I disagree. In your case I'd say "minor difference" arguably not worth the money to upgrade.
**GOOD ENOUGH**??
We're rapidly approaching the point where onboard solutions are so good that we can't tell the difference, when paired with quality audio drivers, to the best DAC's available. We're not there with basic solutions, but I think we're likely VERY CLOSE for your motherboard.