Hello again Andy!
Have had this a couple of times. On one occasion - as mentioned on a certain other thread recently! - it turned out to be botched memory. Same scenario as you, rock solid for several weeks, then a scattering of bizarre errors, including this one.
I'd first try running everything at stock - though you've probably already attempted this

. If no luck, then try memtest.
If the memory has gone bad, it could well be because you're in the Striker's (680i's) <2.3v "dangerzone", even though numerous manufacturers happily certify their modules to run at these higher voltages, it seems they have serious issues doing so on the 680i chipset and simply buckle over varying time spans. Of course, this may not be your problem at all, but as stated, it has visited me several times over the past few months and I've only recently managed to isolate it. The only solution was to find memory that was able to operate at below 2.3v and add active cooling!
As far as potential software/driver causes, as you've gathered, the possibilities are virtually unquantifiable.

I see you're on Vista x64, which I don't have a lot of experience with. I assume you have the very latest x-fi driver - I ask as Creative have only just developed a truly stable one - I was using modded Auzentech releases up until two weeks ago!
Memory "leak" problem perhaps?
I know Vista has tons of video card/memory address related patches.
KB936710, KB938194, KB938979, KB940105, KB945149.
Don't know if all those relate to x64 though. Oh well, I've tried!