Somehow after installing the updates required by Focusrite, my Scarlett 18i6 shuts down their Scarlett MixControl 1.1 software as soon as Sonar accesses it. So I am completely down! After several iterations of installs (i.e. going back to earlier versions etc.) I am still unable to get the audio interface to work. I did notice this morning that the latest release note states:
Known Issues:

- Not passing audio when connected to some USB 3 ports
- "Dim" and "Mute" buttons in Scarlett MixControl affecting level of 'Grey' outputs
- 64 bit DAWs cannot open Scarlett Mix Control using their "Control Panel" audio options (Windows)
DING!
So it looks as if the 64 bit issue is my problem. If any of you are using a stable Focusrite interface on 64, DO NOT UPGRADE your firmware, MixControl etc. until this gets resolved!