Don't forget DPL II when set-up right can do a good job of decoding old SQ and QS quad surround recordings w/o having to use any of the old finnicky 70's quad gear.
If you wanna try here's the approx settings you need to set on yer DPLII;
Center Width (range 0 to 7) : 7 (this effectively turns the center channel off)
Dimension (range 1 to 7) : 4 (this offers equal front/back balance)
Panorama (on/off) : on (more on this later)
Lots of 70's quad surround titles were mastered onto cd w/ SQ/QS encoding intact even though you won't see it on the cd jacket
Check here
http://members.cox.net/surround/quaddisc/quadcds.htm
