Sound error on Steam Version

[BenEaton4]

Okay folks, some technical info first:
Windows 7 Pro 64-bit
4GB PC8500
2x 500GB Seagate HDDs
EVGA nForce 680i
EVGA GeForce 460 GTX OC 1GB
X-Fi Fatal1ty Platinum Championship

I pre-purchased and starting playing this game on day of release (loving the Steam pre-load). The game runs fine (except for the small black dots over characters when DX11 tessellation is enabled).

After anywhere between 5 and 30 minutes of play (it changes) the sound cuts out entirely. If this happens during a conversation, the characters stop talking and I can't get out of the conversation. It's as if because the sound file doesn't play the trigger isn't sent to the graphics system to continue the animations.

So, I updated the X-Fi drivers (they were out of date, but Creative's website is a nightmare to find the most current drivers!). I also updated my motherboard drivers, as they were one point release out of date. My graphics are the most current driver.

Same problem.

Trying a different tack I have uninstalled the X-Fi drivers and disabled the hardware. Then in my BIOS I have re-enabled the onboard Realtek Audio HD chipset on my motherboard, and installed the latest drivers for it from EVGA. This seemed to fix the problem and I put it down to Creative's shoddy X-Fi drivers.

Then it started again this morning, the timings being slightly longer between audio cut outs.

Any help would be appreciated - if there's anything else you need to know, please ask!

[BenEaton4]

Apologies - forgot to give processor specs:
E6300 Core 2 Duo 1.86GHz overclocked to 3.19GHz (giant Zalmann air cooler helps!).

Internal temps - CPU never goes above 60C under load, while GPU fluctuates between 40 and 70 depending on load (tends to be lower under DX11 oddly). The PC was dusted out a couple of months ago, with the processor reseated and new thermal paste applied (old removed obviously and it lowered operating temps by around 10C).

All the different clocks on the board are unlinked e.g. memory clock and FSB run independently of each other so each can be overclocked. The memory isn't overclocked but has had its voltage ramped up to 2.1 from 1.8 but that is in line with Corsair's recommended voltage for these memory modules. They've been in for a year anyway.

Everything else plays fine, normally high or ultra settings, no crashes. It's only DX:HR that is having issues. Anybody got any ideas?