Here's the "old school" trick for splitting a guitar to two amps... If either amp has two inputs on one chanel, plug the guitar directly into the amp (any efx between the guitar and amp will be heard through both amps) then use a second cable conected from input 2 on the first amp (add any efx pedals here, they wont affect the first amp) to the input of the second amp. Each amp can be set however you like without having any affect on the other, this works great if (for example) you want amp 1 to be clean and amp 2 to be dirty or one amp clean and one with efx. I've been using this method for years and (so far) never done any damage to any amps by it. Just be sure both amps are grounded and have matching polarity or you will get a lot of hum.