I was talking with some people the other night and heard about a box called loopback it allows you to run two heads into a single cabinet and then be able to switch back and forth or combine the two imputs without distortion. (inexpensively) I may have the name wrong but if anyone has heard of this I sure would like to learn more.

I'm not sure what it's called either, but I know the technique of using an A/B switch (that is, your guitar cable going from your guitar to a switch that allows one or both of two outputs to be sending signal out to one of two amplifiers). Basically this enables you to play through 2 amps at once, with very different tones for each. Or, you could switch between one or the other.

This requires you to have two speaker cabinets or two combo amps to connect to; I haven't heard of using one speaker, unless it accepts inputs from 2 different sources (maybe some do...)