At one time I ran a pseudo quadraphonic setup with four speakers. The speakers are wired to simulate quad by wiring them to utilize out of phase information. The details are probably available on line somewhere. It’s pretty cool. I also ran four speakers with the digital time delay unit I had for a while.
Does anyone play two pairs of speakers at the same time?
I have found that certain combinations of speaker pairs produce a better sound than the single pair alone. For example: Klipsch Quartets and PSB Image 4T (new tweeters from Vifa) Quartets inside pair and volume matched to PSBs. I have done this over the years and found some great combinations.