This may not be the right area to post this in, but I'm not sure where else it quite fits. I've got my iMac and recently moved my Yamaha P120 digital piano into my office. Since I have some nice speakers for the iMac, I want to use them for the piano as well (its internal speakers aren't so great). Going through the line-in on the iMac is not an option...it's laggy and is just generally inconvenient. I have a couple headphone Y-adapters...so one end would go to the speakers, and the other two would go to the iMac and piano, respectively. My question is about using that Y-adapter. Is that bad for any of the electronics involved? I have a friend who is an electrical engineer, and he says I shouldn't do it. His reasoning is that the iMac and piano are both pushing out signals (power), and the Y-adapter turns what is normally a 1-way street into a three-way traffic jam. He says that since any output signal coming from the iMac would go to both the other ends on the adapter, it could damage something on the ports on the piano that are only designed to output and not input. Same is true, he says, if the piano is outputting audio and it tries to go into the headphone port on the iMac. (Just to verify, this is indeed true of Y-adapters. They do not discriminate about where the input signal goes. It just goes to the two it didn't come from.) Now, yes, he is an electrical engineer, but he's also kind of old-school and ultra-paranoid about some stuff like this, which is why I want to get a second opinion here. I'd appreciate it if anyone has any definite knowledge about this.