Lets see your listening room dimensions.

2 rigs. The Quad ESL near field is one corner of 40’x26’x7’6" with beamed ceiling basement. The other system is the corner at the other end but is actually almost half the space at the other end.

I happened along this thread and am looking for advice.  My system is currently in a very large room 25' x 35' with 8.5' tall ceilings and it sounds awful.  Why, because my house is a mid-century modern built in 1959, and has solid brick interior walls.  Additionally, the right side corner and wall is mostly glass.  The back of the room is open but also has a glass divider.  Lastly, someone installed a large skylight that is over the left speaker.  Since this is the main room we live in and you see when you enter the home, treatments are not an option.  So, I have decided to look at other spaces in my home.  The first is my office that is 10 1/4' x 20 3/4' long, the next room is 12' x 13.5', both with 8.5' ceilings.  The office would be ideal but I don't know if the dimensions will work.  I can put as many sound treatments up to compensate but am concerned the 10' width may be limiting.  Very curious to the groups thoughts.  Thank you in advance.

Try the 12' x 13.5' one. My room is fairly close to that one, dimensionally, and I've managed to achieve a very balanced, natural sound.

As far as dimensions go it is best to avoid multiples, especially the same each way. 12x13 is very nearly square. This room will have the same big bass modes L/R as F/R. The other room 10x20 is twice as long as wide which is less bad and also the extra length opens up some options. You could for example build a wall across one end shifting it to something like 10x17 cleverly using the space as both storage (component, records, etc) with the space behind as a bass trap. Mike Lavigne does something like this in his room. A guy could do worse.  

Doing it this way the width is 17. Put the speakers on that wall, about 2 feet in and you sit a foot or two from the back wall. This gives you real wide space off to the side for awesome imaging and puts you about 7ft from the speakers for a nearfield experience that will require a lot less power. Especially since sitting near the back wall will give a lot of natural bass reinforcement.

Mine is a dual purpose music and audio room.  the dimensions are 20.4 feet long 13.4 feet wide with 8 foot ceilings.  Speakers are approximately 8 feet apart and 4 feet from the front wall.  Listening position is 10 feet away with 7 feet on the back wall.  A few treatments have helped such as bass traps, diffusors, HFT's and Townshend podiums for the speakers as well as component isolation.