All you need is a simple hum eliminator/isolation box inserted on ONE of your lines to the amps (left or right). Don't be fooled, some boxes have two parallel lines through them (two inputs/two inputs): that's for stereo into one amp/mixer…with that sort of box just use one side of it, into ONE of your amps… has worked for me for many years. Don't have the box close to your amp though, that can create another hum problem. Sometimes it's better on the left, sometimes the right.