I suppose that to get a suitable music stream fed into my new Ethernet only network bridge device, a simple extender will do the trick. I think that device just sucks in the existing wifi signal broadcast by the main wifi router, and feeds it into an Ethernet plug. So basically, this is fundamentally using wifi to transfer the signal.
The mesh systems seem to set up an alternate, more powerful broadcast-and-receive setup using wifi also. Not sure if that’s on different frequencies than the basic repeater gadget above which simply sucks in the existing wifi signal. Yes I see that some of these mesh units give you an Ethernet jack at location B and some don’t.
As I understand it, the Ethernet over Powerline arrangement is totally different. It is a wired connection only (never goes through the air) but these EOP devices specially encode and then decode the signal so it rides on top of the 110 AC lines in the walls. So fuse boxes and other barriers can present obstacles for this ride-on-top signal to get from the transmitter to the receiver unit. I wonder whether this encoding/decoding process degrades the music being sent, AND whether running those signals on top of the AC power also dirties that power feeding the hifi gear which may be sensitive to it. So this introduces that new problem.
Seems like all CAN work but not sure which would deliver the best sound quality and least errors and most bandwidth. And if the EOP dirties up the power to make the rest of the system sound bad.