I don’t think you need a preamp. I connected a record player to the Sonos Port so I could hear it to the Arc. What you should be careful of is how you would connect the Port to an old CD player. My record player is new. So it connects into the Port via a red and a blue plug. If your old CD player does not have this best to call Sonos helpline.

Generally speaking that scenario should be possible due to fact that Port has a set of analog RCA inputs that allow you to connect devices like turntables or CD players. Simply connect the RCA cable from your external audio device to Port’s RCA inputs labeled IN and play out of your Sonos system, so no preams should be needed.