For SQ recordings you really need a decoder, but, if you have a couple of extra speakers, hook them up in series with each other, and "bridged" across the Hot terminals of your stereo amp and put them in the back of the room. You will recover some, if not all of the Quad effect.
Matrix multichannel can really work, but was born prematurely and died. It should have implemented Left/Center/Right/Rears channels (not Left Front/Right Front/Right Rear/Left Rear) and the gain-riding logic needs to be digital (which was not possible at the time). With digital implementation the signal that you listen to can be delayed slightly while the logic analyses it. In this way the gain adjustments that enhance separation do not always lag behind the music, giving a "Pumping" effect.
Matrix multichannel can really work, but was born prematurely and died. It should have implemented Left/Center/Right/Rears channels (not Left Front/Right Front/Right Rear/Left Rear) and the gain-riding logic needs to be digital (which was not possible at the time). With digital implementation the signal that you listen to can be delayed slightly while the logic analyses it. In this way the gain adjustments that enhance separation do not always lag behind the music, giving a "Pumping" effect.