Well the channel cloning/multiple modes is only on the two-channel models, but basically it means that there are 3 distinct channels available on the amp (clean, vintage/variable high-gain, and modern high-gain), and any two can be footswitched between (or you can duplicate one of those channels). So in other words, you have two footswitchable channels (and sets of tone knobs), that I'll call top and bottom. Normally, the top is either clean or vintage high gain (controlled by switch #1 on the back), and the bottom is modern high gain. However, with switch #2 on the back, you can either a) make the top channel modern, b) make them both normal, or c) make the bottom channel vintage. But the thing is, the controls aren't totally independent of their channels, which means when you make the bottom channel (normally modern) vintage (with switch #2 option c), for some reason the presence knobs on both channels are apparently active, which is supposed to yield more tonal possibilities (perhaps think of it as channel 3.5) - I have yet to mess with it, but will soon!
