I don’t know about extra pairs of speakers playing together but I recently heard the Swarm type subwoofer setup and bought it immediately. Multiple subs setup right is incredible sounding.
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.