Unless you have the wiring diagram for the factory stereo system... yes, they are correct.

However, you should be able to utilize the existing amplifier.

The output's of the stereo are listed in the service manual.

Here is a screenshot of the wiring diagrams. I've highlighted the area you are looking for. The pre-amp outputs of the stereo and the amp trigger is all you should need.

I would recommend a meter to find the hot and ground in the existing stereo plug unless they are providing a harness adapter.

EDIT: Now that I re-read the diagram and the following pages in the manual as well as the becker site's pinouts for the Indianpolis Pro (same as the factory stereo for wiring), it appears the amp is using speaker outputs. The pre-amps outputs of the factory stereo are NOT being used in the OEM Crossfire application. I have added an additional picture showing (in yellow) the speaker outputs from the head unit and (in green) the power and other pintouts.

NOTE: The 'trigger' going to the power antenna only applies to the roadster... it should not apply to the coupe.

Hope that helps!