Very good write-up sir!
You've clearly done a lot of research on this - did you find a way to test the amplifier in any way before installing? I have a problem with my DAB radio reception which I've written about in a different thread. I suspect the amplifier is faulty (no fault codes though), but haven't found a way to test it. I have tested the DAB-radio with external aerial - worked fine, but like you I would rather keep it OEM.