You guys might find this interesting. I was looking for info on the device I had in the early 80's, which turned out to be the Sound Concepts Image Restorer IR 2100. Came across this interview with Ken Kantor, who according to his statement in the interview, designed the device. I was particularly intrigued by his comments in the interview on how speaker placement can give some of the benefits.
http://www.kenkantor.com/publication...erview_01a.pdf
Now does anyone know what percentage of the distance you are sitting away from your speakers equals 21 degrees? For example, if you are 12 feet away, what percentage would you use for the distance between the speakers. I might give it a try.
( I hope posting this link is OK. It takes you to a PDF of the interview.)