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.
aburnhamuu
Siegfried Linkwitz designed the Watson SEL to support the Orion.
I've found that they also work very well with the Pluto and LX Mini. www.linkwitzlab.com 
Everything is dissimilar.  The "unified theory" is still yet to be proven.  MOST speakers (in an enclosure) are assembled from "off-the -shelf' drivers from the few manufacturers who mass produce them.  Who defines (and decides) what is "similar?" Virtually most speakers enclosures with their drivers that are commercially available aren't designed to be assimilated into speaker "X."  I've heard systems far into stratospheric price levels with 2 sets of top-drawer speakers driven reference components (every piece $10,000 and above) that were highly satisfying.  Paul McGowan of PS Audio has more than once lamented about the arrogant, opinionated and narrow-minded rantings of some in our hobby.  You can disagree and still be polite and civil.
Pairs of dissimilar speakers? No. Pairs of matched speakers, sure. Double Advents are well known as are double pairs of KLH-9's. Double Quads are another well regarded option. Ever consider that Acoustat 2+2 are really doubled 1+1? Nobody thought that was odd that I remember.
Personally, I run two pair of VMPS Tower II at the same time and have for years. They're side by side thank you and sound wonderful.
Anytime you see "Purist" in this hobby watch out. That's the snob side of things leaking out over the experimenter side. There's no rule that says that two pairs of speakers, similar or dissimilar will sound one way or another. If you have such and want to play about, keep in mind that you might find something you like for little or no cost.
That's how discoveries are made.
"What a stupid idea to use two dissimilar speakers together at the same time! Goodbye coherence!"


Goodbye coherence, hello enjoyment.  
I switch to 7 channel stereo for casual listening at lower to mid-level volume, then to 2 channel for more critical listening at higher volume levels. Speakers are somewhat of a hodge podge at the moment with ESS AMT's for the front L/R, Martin Logan FX2's for the rear L/R, polk center and 2 velodyne subs (15" and 12")… Mostly used as home theater, but the ESS AMT's can rock pretty well in 2.1 channel.


I like the additional speakers at lower volume levels.