Which Denon Amp? Perhaps if you post the model number, we could look it up and provide some assistance. Or, you could post a picture of the rear of the device so we could see inputs and outputs.

In general, the Port should be considered the same as a tape deck, so the Ports’ inputs would be connected to the receiver’s line out, and vice versa. However, things get more complicated with newer amps that don’t have a tape ‘loop’ available. 

Just as a note, you can play FM on the Sonos without connecting it to the Amp at all, using TuneIn, iHeart Radio, myMusic player, or even adding a direct internet stream by following the instructions in the setting up an internet radio station FAQ. 

Hi Here is the connections at the rear and the serial number of the amp

It’s almost impossible to fully connect a Port to this Amp. This Amp just isn’t designed for this. 

You could take the analog out from the Port, and connect it to the Media Player in, or the CBL/SAT input…but I’m not sure where you would get output from the Amp in to the Sonos Port. And as a result, you wouldn’t be able to get your FM from the Amp into the Sonos ecosystem. I’d stick with my previous suggestion, and use the functionality in the Sonos controller to access your FM station(s). 

Thanks for the reply 

What do you mean

use the functionality in the Sonos controller to access your FM station(s). 

According to the specifications of this receiver, there are no stereo analog outputs. Therefore, it would not be possible to use this receiver to feed a SONOS Line-In.

Most stations offer an Internet feed. As suggested above, search for your station online.

You  can add TuneIn, then search for your station.

Sonos allows you to stream radio from your Internet connection. You may have some already available on your Browse screen.

Also: https://support.sonos.com/en-us/services

Kitu

 I note there is a hdmi out to monitor.

With and audio extractor/convertor you maybe able to get a signal into your port.

I'm having similar issue as BBC sounds app is not stable enough to listen. (Drops out regularly) so looking to Connect to mini hifi. My old Teac only has an optical out, but this can be converted to analogue as stated above.

Hope that helps.