OK, I got everything out from under the intake manifold -- not too bad once you get the feel for it. I pulled the old relay-solenoid, and it won't hold vacuum, unlike the new replacement unit I bought. I have been replacing various original vacuum lines and related rubber parts as long as I am in there, but I am confident that my CEL and failure to set secondary air monitor were attributable to the combi valve (which admittedly probably is cleanable) and particularly to its control solenoid.
If anyone needs any AUG 1.8T tips on the disassembly procedure, fire away. I'll be glad to help any time, now that I am a veteran of this. I'll be a couple of weeks late with my registration renewal, but I did pay the fee a month ago to avoid any potential late penalty.