Asus m4a79xtd evo audio drivers

I am running windows 7 premium 64bit and Process Explorer highlights that VIA HD audio causes svchost.exe (audiosys.dll) to start hogging 20% cpu after Driving games Dirt, Grid and LSF if speakers are made default for listening through headphones. A restart makes it go away till the next time.
Selecting ATI HD audio (only available for the HDMI output and works OK) as default does not cause this to happen.
A VIA HDMI output is offered and can be made default but even though volume controls indicate something is playing, no output is heard.
Updating to the latest VIA 6.0.1.7900 driver did not make this go away and stopping VDeck did not help.
Suspending audiosys.dll makes the hogging stop but then the programs will not start.
I there any way forward? Playing these games with the tinny sound on my monitor is no way to go.
Cheers Don

Update:
I found that audiosrv.dll was missing from windows/system32.
I copied it from windows/winsxs and all appears well. The reported size of it was 0 and is now correct at 661KB. No idea how this was missing.