CD changer installation

Hello.

I recently got a used S8 (98) which unfortunately only has a radio with cassettes.
I assume that in this forum several have already installed a CD changer and have the following questions to these users:
1) Is the connection cable between Radio Concert and Changer already installed in the car? (The small blue CD plug is present on the radio, but unfortunately I can't find the round 13pin rear left in the trunk)
2) There are CD changers with 2 different Audi part numbers, the 4B0035111 and the 4D0035111. Which one is intended for an Audi A8?

Thank you. Greetings.

Jean-Claude