@husker. Thx for checking, it is helpful.
I used to be able to disable the HD Audio bus/controller (thx to CA for noting the issue) and DAW performance was flawless for the longest time. I generally try to keep Win10/SONAR updates coordinated but the Nov update seems to have disrupted the equilibrium. Both the Win10 and Sonar updates were checked out on a sandbox PC before upgrading with NO problems there, which has me looking at any cfg issues in detail on this DAW.
Some of the registry keys for NVidia were referencing amdx64 somethings which is why I was trying to root them out.
Still working on a robust configuration for the US-20x20. Still seeing audio dropouts when speed comping fairly heavy vocal stacks. Could easily be a sonar buffer/tascam driver setting, but these projects ran fine before. And yeah, doing additional file housekeeping to eliminate that as an issue (save as cwb, etc.).
I'll post an update if I can come up with anything definitive.
Thx again.