I have a Boss BR1180 with two powered monitors connected in the back via RCA jacks (Left and Right). As far as I know, there is no way to mute the monitors. So the sound from the microphone, for example, is coming out of the monitors all the time-- while I'm recording and while I'm playing back. Is there something I can buy to place in between the monitors and the Boss unit to mute? Something not overkill? Thanks!