Does anyone play two pairs of speakers at the same time?

The "speaker for each" instrument was the point of the Dead's famous "Wall of Sound" system back in the 70s. So it has been done. 

i have 4 speakers from the '4 chanell' days so i use all 4 in my 2 chanell system!!!

Why stop at four, one of my systems has 15 speakers and four subs. I even have a special name for that system. Home theater room. Sounds wonderful. Lol

I run a pair of AR3's horizontally stacked with a pair of AR3a's. The 3's are driving by a McIntosh MC2300, the 3a's a Mc MC2105. Both amps are fed into a Mc C22(original, not reissue) preamp(with Y IC's), and the preamp is connected to a McIntosh CR7 remote which is how the overall system volume is controlled. Doing this because I have the gear lying around and no place to set up a second system, but more to the point it sounds better. A lot better. In every way. And yes, it sounds excellent using just one amp to drive either pair of speakers. I pay little attention to so called experts on stuff like this because at 64, having been involved in audio since I was 15, and listening to and owning all kinds of gear, I trust my ears with harmless stuff like this. Works for me.

Like the hippies used to say, "if it feels good do it."  Note: that doesn't apply to scratching mosquito bites.  But as for me I prefer a single pair of the best speakers I can build.