I understand that there are a myriad of ways to wire up three way switches, but that's about as far as my knowledge goes. Here's my issue. I've got three cans which are currently controlled by two 3-way switches. I want to add two more switches to control this same set of lights. Access is fairly good in that the walls are open to all but one light and one switch. What is involved in adding these 4-way switches? I'll draw up a diagram if necessary. Thanks.