Well I just installed some ear buds in the helmet and ran the wire and connect to the RD. I am tethered for the moment but hardly notice it while riding. I snake the wire from the helmet down the inside of my left jacket sleeve and plug into the RD jack (RD on left side of bike).
I didn't want to spend a ton on the Sena unit since I don't listen to music when I ride or use an intercom set up and I gather that the cheap transmitter and receivers that I mentioned earlier would not be reliable with an intermittent signal from the RD.
For years I rode with one speaker in the left side of my helmet with a wire connected straight to the RD. Didn't even run it down the sleeve, just let it lay down behind the tank bag. Worked great and when I got off the bike just unplugged it from the RD. Cheap and easy.