I have read in several places that it is generally a bad idea to connect an instrument directly to two amps. The argument is that the amps may be at different ground levels. This could cause a potentially lethal voltage. Lately, I heard another view on this. About a week ago, I was in a store run by a very knowledgable and respected owner/player. While I was trying out some basses, he was talking to an amatuer player who wanted to hook his bass up to two amps. The owner sold him an standard A/B/Y box. I was a little concerned that he gave the buyer information that could be potentially hazardous. I did not want to upset the sale, so I waited until the customer left. At that point I mentioned to the owner that the solution could be potentially lethal. He said that if one of the amps has the ground lifted, there is no chance of shock. It doesn't make sense to me, but I am not expert on the subject. Is what he said true?