As promised, I am reporting back with the results. I returned the tuner to SONICblue (UK) and Hugo got it working. He reported,

"...we think it may have been a stray bit of solder causing a join where it shouldn't."

I re-installed it the same day I received it back, and it has worked flawlessly for a week now. It was well worth getting working, since it does make it much easier to operate all the features of the empeg while still keeping my eyes on the road. My thanks go out to David and Hugo for all there help!