One further thought. Mixcraft doesnt use ASIO by default. And if I open Mixcraft using Wave or WaveRT drivers, rather than ASIO, I still have a problem.

That is, if I open Mixcraft without ASIO its OK for sound, and then on opening Biab I get an ASIO buffering errror message, even though Mixcraft isnt set for ASIO drivers.

Other way about, if I open BiaB with ASIO its great, but then open Mixcraft I get a sound error message - although this seems to relate to the device ie speakers rather then the driver.

I wonder if this isnt a driver issue, but a device sharing issue. Oddly, under Windows / control Panel sound setting there is an option to give apps exclusive control over speakers. But I've disableds this ( and restarted) and still have the same problem.

The curious thing is that if I open Mixcraft and then Biab the message definitely says ASIO driver problem - but maybe if it cant access the speakers, it shows as a driver problem?

That would explain why ASIO multiclient doesnt help.