Sorry It's just sometimes on this forum you try but because there's more than one of us helping it gets real hard to follow what was done and even at this point I'm not sure what is not working.
My understanding was you were loosing the connection to the Tascam when you opened Sonar.
This is a common issue on some systems and the normal fix is to disable all other drivers.
But then you and Bob are going on about what might be an unrelated issue and PDC?? that lost me so therefore I thought my post was a waste of time because I wasn't sure my information was still on topic,, that's all.
So what is still not working? It does sound like your getting things sorted.
If the Tascam is always showing in Windows audio settings that's a good sign.
Sometimes these issues are as dumb as a bad USB cable so step by step. I'm optimistic that there is nothing wrong with the interface and once working you'll be rocking..