for those interested I have found the solution.
This was tested using only the ASIO driver along with 2 audio interfaces: Line 6 GX (non studio), Steinberg CI2. Both have their drivers completely up to date.
OS is windows 7 pro x64. 16GB RAM and AMD CPU.
When switching between inputs & outputs the application needs to be rebooted. No reboot means that the metronome will not work. I assume the application assigns the metronome output on boot and not during the input/output switch. But I can only guess.
Also, using too many FX will also cause the metronome to not work. I learned about using stereo buses (which has caused me other problems) and this helped me to reduce my FX count significantly.
Since I have located these two problems I have had no dramas with the audio metronome in Music Creator 6.
I hope this helps whoever happens to read it.