I just put the captured dodgy file through MSE, Kaspersky, and Trend Micro, and none of them reported it as being malware.
If none of these AV programs can detect malware, what's the point of running it at all?
That is because the "dodgy file" you refer to is really part of DirectX. See the file listed here. There is some other executable that you missed that is the real culprit.
Seriously, running something like MSE takes no noticeable resources, and I run some heavy duty realtime music applications at low buffer latencies without any audio glitches. And I don't see what the big issue is with leaving UAC turned on. Once in a while I have click on "Yes/No". I really can't remember the last time I had an infection, it has been years now.