Hi Tim,
Im also new to this forum and also new to owning a A6. I have had a similar problem in so much as I cannot get any heat out from either side. I have tried the usual suspects and no luck so took it to a local garage who have manged to get some heat out. They flushed out the heater matrix for both passenger and drivers side and refilled paying careful attention to getting as much air out as possible. I now have heat but they want me to go back next week so they can use a vac pump to make sure there are no air locks. Seems that air locks in the system are a real pain on these heating systems. hope this helps