I have also for a couple of years been wondering why this solution is not ready for the world yet. It seems like an easy task. The technology already exist the other way around. Sending from the musician to a reciever (guitar, bass and vocals). I'm thinking about the Relay systems. Basically it is a digital Wireless signal flow from one place to another. Why not the other way? It's just a signal flow. I cannot see why a signal cannot be directed the other way. Think of it as you're wearing the reciever in your pocket and placing the transmitter in the rack. Reversing the flow. Instead of a guitar signal you put a line signal from your mixer in and you connect your in-ears to the output of the reciever instead of plugging it in a guitar amp. I really do not see the big issue. But I'm not an engineer so I don't know, if there is a problem somewhere. But this is 2015. We landed on the moon 50 years ago (or did we :-) ). But please get it done!