Get a cast-enabled amplifier then? Sony's receivers cast built-in, for example.
But you realize how extremely niche your problem is, right? That there clearly aren't enough of people in your particularly situation who also want a dongle that haven't already bought one?
I have a top of the line amp, why do I have to get a "cast enabled" one? I am not sure what the last sentence meant. I already have the dongles, I'm just sad they are no longer going to make them.
But you realize how extremely niche your problem is, right? That there clearly aren't enough of people in your particularly situation who also want a dongle that haven't already bought one?