You could connect a PORT as if it is a cassette deck, however, there will be a frustrating detail. When you are playing Phono or Tuner on the console, all of the SONOS Rooms using REC OUT will be delayed by 75ms. This will be an issue in any areas where you can simultaneously hear SONOS and the console. While I did not see any in your photo, a console “Tape Monitor” function could work around this.
With respect to radio stations, most currently have an Internet feed. You could play SONOS Internet stations from “Tape” (Line-Out) and avoid the delay.
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A completely different approach could use a SONOS AMP connected to the console’s internal speakers rather than the console’s internal amplifier. This would be practical only if the console’s speakers can be hooked up to AMP as regular 4 or 8-Ohm speakers. The console’s Tape Output would be connected to AMP’s Line-In RCA jacks. You would use the Line-In to play Phono or the console’s Tuner. This will not work out if the console’s speakers use a vacuum tube amplifier.
With this scheme you will avoid the 75ms Latency issue because all of the speakers would be driven by SONOS,
