[notorious]

Knee panel is easy to remove. And you can drive without it. I now drive without it no problem.

There are several candidate locations available in that area, where we can mount receiver with a stock bracket or just use cable tire, etc.

I think stock bracket is actually used as spacer. It seems antenna doesn't like other large objects (no matter steel or plastic) in immediate vicinity. This is why installation in visor didn't work I think.

Mounting antenna properly spaced takes time, i.e. if we want to mount on a bracket to structural beam from under knee panel we need to drill a small hole for screw, and/or use adhesives i.e. putty.

Cutting cable in half and adding extra length in the middle is no problem. Like I said, Audi now route same 3 wires to rear bumper. However, with standard cable length you can get pretty much everywhere in driver's footwell. Another interesting location is under driver's footrest. It is completely hollow inside and there's loads of space in it. I'm only worried it may not be high enough.

Inserting connector into back of cluster is very easy with knee trim out. No need to remove cluster for that. Pulling it back is easy too. I see no need for additional connector in the middle. BTW, 3 wires are: Black is ground, Red is power +5V from cluster, yellow is clock data pulse.