Quality of 70s Quad Pressings?

I picked up a few 70s CTI jazz Quad SQ pressings. They sound pretty good except for what seems like a lack of bottom end. Any of you techie types out there care to enlighten me on the process used to get four channels out of the grooves? According to the sleeve only a decoder is required, not a special stylus.
That's right, you only need to find a decoder and hook up to another stereo amp and two more speakers. I still use an old (1976) Lafayette decoder, which has decoding for SQ, QS and some composer (basically the Hafler circuit) positions also.
Depending on the records, sound isn't bad.
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.