Thanks for the info - I suspected that was the case, but also thought it may have been down to laziness/ineptitude on the part of the installer. I'm guessing since the S8 DIS must've been a good couple of years ahead of the A4 level installation it has slightly different characteristics.
I think on the bluetooth front I wasn't helped by the dealer starting the car to get it out of the showroom so didn't get to fiddle before we were ushered out for our drive! Was worth it to stand behind the car when it was fired up down those Milltek pipes though
Just need to sort a price out and figure out how to stretch my garage by 3" while still giving me enough storage space....