I'm shooting a music instruction video and have voice and two instruments, so I put the main instrument on one channel, and the voice and other instrument on the other channel. A problem I cannot seem to overcome is that the mic (Rode) picks up more than just the voice. Are there any tricks to overcome this annoying issue?

The other problem I have is that annoying feedback sound from the mic to the speaker *waaaaaaaaaa* that gets louder and louder. The only solution I've found for that is to use a mixer that allows me to just unplug the channel that the mic is on so that the mic isn't going out through the monitor speakers.

Does anyone know of a rack mount 4+ channel mixer that will allow me to disable the microphone sound from coming out through the monitors?