Thanks for the suggestion vespesian,
I enabled the onboard audio, and got the generic ASIO driver working with it.
Loaded up may ‘test’ project in cubase and it ran through the song about three times before it failed! Exactly the same issue.
I think it has to be a system issue of some kind, but I can’t guess at the right bit. I’ve updated OS, drivers, versions of Cubase, audio interface/drivers, changed every bios setting that I understood, changed system drive, added memory, removed all third party plugins (although they are back now…can’t get by without waves), turned off core parking (yes, I was that desperate)…and still it only exhibits the problem with Cubase.
From some of the behavior shown in the resource monitor graph, it looks to me like the process shuts down briefly and then goes to 100% (and the system locks up) briefly as it tried to recover. Perhaps Cubase allows the processors to think they are idle and halt in some way that interacts with the way my power management is set up…may have to play with the other BIOS settings (C states etc) and see what happens. Unless anyone one else has a better suggestion (PLEASE)