I can't seem to enable the ASIO drivers for my Komplete Audio 6 interface since they are greyed out in the Sonar 8.5 dialog.  I was able to enable them initially but when I exited out of Sonar and went in again they are no longer available.  Note that I am able to use this interface (ASIO drivers) in Guitar Rig 3 that came with Sonar as well as the Cubase LE application that came with the interface.  Any ideas why these are now greyed out in Sonar? 

My guess is your on board sound card is interfering. 
Sonar is the king of picky when it comes to drivers as you noticed. 
So best bet is disable the on board and then make sure the Komplete is selected as  default in your windows control panel Audio Device dialogue. 

Turns out it was simple: I had to disable the the default ASIO driver in both the input and output driver lists before I could then enable the Komplete drivers (they became "un-greyed").  I'm guessing installing Cubase installed some "Generic low latency ASIO driver" which were the default when I reopened Sonar and might be why it worked in Sonar initially when I hadn't installed Cubase yet.   In any case, thanks for your help.

Yes you cannot have 2 ASIO drivers active. That was my guess that your on board was the selected one. But it is best to disable it so this will not keep happening, you don't really need an onboard card.