I live in Canada. You're asking me about an American franchise store. I don't hear things that give me great confidence in their staff, but really, I have no personal experience with them.

Nobody runs a half-dozen amps at once any more. There's no need for it. For two, a 'Y' cable or a 'Y' adaptor connects one signal source to two amps. If you ever get hired to do some kind of retro gig where you need to look like you have a wall of amps behind you, I guarantee that most of that stuff will be dummy cabs. The soundman will only mic one or two individual speakers.

There are lots of booster pedals on the market. They're usually intended to overdrive the input of an amp to make it distort, but the main thing is that they raise the voltage from the guitar. The amp input is usually at least 1 Megohm, so any active pedal can handle driving several amps without any trouble at all, even if it isn't meant to act as a booster.

Tony Iommi's rig was typical in this regard. If you plug a guitar straight into two or more amps, you may notice some reduction in the high frequencies, especially with low-output single-coil pickups. But you'd be loosing some high end any way, because of the long cables. You don't run multi-amp stacks through a 10-foot cable! Note the treble booster Tony used.


{Edit Note: I got tired of getting the same questions from the same guy on two different threads, so I merged them.}