Hi there @Misterb89.

Thanks for reaching out and welcome to the community! Let me help you out.

Do you already have an existing system or are you setting up your Sonos system for the first time?

If I understand it correctly, you want to set up Sonos Arc and Amp as a home theater system? 

Assuming that I understand it right, you will use Sonos Amp for the in-ceiling speakers so you can incorporate the Amp to Arc.

You must set up the Arc using the Sonos app before it can play TV audio. Note that Sonos Arc requires the S2 Sonos app. You need to connect the included HDMI cable to the TV’s  HDMI-ARC or HDMI-eARC port. The Sonos app will guide you on which cables and ports to use when connecting your Arc to your TV. This article will help you get started with setting up your Sonos Arc. You can find more information on product features and specs on the Arc's product page.

Once the Arc was successfully set, then you can add the Amp to your system. To use Sonos Amp as TV speakers, you can select As TV surround speakers when asked “How do you want to use Sonos Amp?” during the setup process. For more information on using your Amp in a surround setup, see our article on adding surround speakers.

NOTE: If you prefer to set up the Amp “in a new room” or as standalone (not bonded to Sonos Arc), you can group two or more Sonos products together to play the same content.

Let me know how that goes.