No - you just don't! I have never, ever heard of this kind of thing damaging equipment, because accidental shorts are far more common and never cause grief. Think about jamming a guitar jack into a headphone socket - grabbing the wrong one in the dark. Music gear knows stupid things happen and make sure warranty repairs don't result. A simple Y split has never let me down. How many people have accidentally connected two items together, like two mixers - as a submit - with the mixer out going to an XLR in - but forgot to turn off the 48V phantom. Odd things happen - like LEDs all coming on, but never damaged anything. Forums are full of "will I blow up my XYZ?" and in all my years as I said, I've never blown anything up! In fact - back in the early days of Hifi - 73 onwards, everyone was bodging up cabling to connect their new stereo recorders to their mono amps, and mono devices to stereo inputs. To be electrically correct, and do it properly, sure - solder them up with a resistor, but in practice, you can connect anything to almost anything and with a bit of care - like starting with gains down and faders down - most things can be made to work.