I've now got a uses amp for an E46 with Harman Kardon.
I then removed the connector:
Here you see the connector after removing it from the print card:
Here is the part number. This is impossible to order. I assume that this is the reason Technic go ahead and created on by himself.
Here is wiring diagram for the power and signal. This connector is the X10266 on the diagram:
I'm now going to soldier on RCA, speaker and remote on wiring to this connector. This is basically the same that Technic is creating and I would recommend buying it from Technic instead of creating one. I would be much easier.