I have a 2x12 cab with a couple of 8 Ohm speakers wired in stereo. In other words, one speaker for each of the two jacks. I've seen Marshall cabs that have a little switch in the back that allows you to choose between 4 Ohm mono, 16 Ohm mono and 8 Ohm stereo. How the heck do they do that? I'm not adverse to installing a switch or two into the back of my cab. Switching jacks if need be too. I'm also open to slapping together a little switching box to do it between the amp and cab. I just don't know how to do it. Anybody have a source for a wiring diagram for this? Or, if possible, anybody know a source to simply buy one of those Marshall cab jack plates?