I would run resource monitor and see where you have your exact (as close as that will get at least) problems. Make sure that you have the symlinking working on your wow setup and the processor affinity worked out.

I would also try disabling sound entirely on the system, device level not just muting and see if that works. There are race conditions with software heavy drivers and each wow is going to make a new thread on a different processor if it can and all that noise.