Don't give up on us just yet.
There is no reason I can think of why using a single audio interface and setting things up for it should end up with no sound, so I think that deserves revisiting.
Please detail any and all steps in making and testing your testing of the use of the single interface.
Also, when you made those changes - did you test it using a new project? (A nice simple import and playback of a WMA/MP3 audio file to an audio track, perhaps)
And, did you make sure to power cycle your audio interface after making the ASIO Buffer Size change to 128? (It is recommended to do so after making settings changes).
Thanks for hanging in there - we will collectively do our best to help you figure this out. My rationale in asking for the single interface ASIO testing is to get to a place where the dropouts are gone, and I believe it likely that the use of a single interface, configured with Sonar for ASIO driver use, should be able to do that.
I look forward to hearing back from you with the details on your ASIO test of the single interface.
Bob Bone