Hi @mcleand
If you have an Era 100 and adaptor, with an RCA output from the receiver connected, you can play that input to any other Sonos room wirelessly - this has long been a feature of Sonos systems. The Era 100 does not even need to be playing - Line In will appear in the app as a source for all rooms to play.
Using a Port would look a bit “cleaner”, I suppose, if you had no intention of using the Era 100 as a speaker in that room, but it would work the same for this use case. Using a Port instead (if the output on the Port is connected to an input on the receiver) would also allow the receiver to play along with your Sonos system.
If you plan to play your turntable to both the Bedroom and through the receiver at the same time, and if you are able to hear both at the same time, I’d then recommend the Port - if your receiver has a tape loop/monitor function - as the turntable audio would go through the receiver, get amplified to line level, go to the Port and get digitised and buffered for network play, then go to Bedroom and play, but also feed back through the Port, back into the receiver as Tape Loop/Monitor and play through the speakers connected to the receiver in time with Sonos. This presumes that the receiver does not introduce any additional delays, however. This is not all that common.
I hope this helps.