Okay did some further testing last night. Also update Belkin and Net Extreme drivers.
Completely removed from system (driver sweeper on creative sound too):-
Both of these items have a questionable win7 support.
I also did some further synthetic testing - multitasking with WMC live play, Firefox on HD you tube video (seperate monitors), malware and antivirus running scans in background. These were the conditions causing the BSODs before. So far so good. Using motherboards onboard sound controller.
I'll stay like this for next few days and see how it goes.
Thanks all for the help - much appreciated.