You don’t want to send an amplified output to a port, you’d be better off feeding it a line level output from the amplifier, such as a tape out. 
 

You’re intending to use this amplifier as a switch for what you’re feeding to Sonos? Note that any speakers connected to this amplifier will be slightly ahead of any Sonos speakers. 

Hi there, thanks for the response. Still a little confused, do i connect Turntable and CD player to external amp and then a line from the amp to audio out on the Port to be able to play as a switch through Sonos ?

Leave the external amp out of the setup and just use an RCA switch like this:

https://a.co/d/9WXuKqO

Certainly easier to do as @GuitarSuperstar suggests, but if you feel you must use the Amp, consider the Sonos Port to be essentially the same as a tape player. Connect it in the same manner, using tape in and tape out. The FAQ for the Port is here. 

The output from the Amplifier/Receiver would have to be plugged in to the Line In of the Port.

My receiver/amplifier has  Zone 2 output rca jacks that can be used to send the signal via wire e.g to another room where it would feed another amplifier. I use the Zone 2 output to feed the Port Input instead. This way, I can stream anything from my amplifier/receiver by selecting the switches on the amp, e.g. phono, CD, tuner. The Port will stream anything selected. For me I’m streaming to a Sonos Move. There is no need to plug or unplug anything, just use the switches on the Receiver. 

Jai

Cheers Jai, this is what I am currently doing, I just have to get the balance right as it is a bit distorted

@Jai67: are you experiencing any lag between the speakers connected directly to the Receiver and the sonos speakers, when you run both zones at the same time? I have a whole bunch (like 10) of Sonos speakers all over the house and would like to run my home theatre speakers (zone 1) with all Sonos speakers (on Zone 2 through the Port, which I am considering buying) - and create a whole home audio arrangement. However, if there is a lag on the sonos speakers, it won’t work.

There's always a 75ms delay when using the analogue input on Sonos. The only way to prevent this would be putting the Port between CD-player and receiver. Since the “out” of the Port is synced with the rest of the Sonos devices you probably would not have a delay.

Thanks @106rallye.