Speaker distance

And that can ONLY be done with a careful long term program of room treatment plus the fabled XLO Test CD speaker placement track IMHO.

@geoffkait 

Hello Geoff. To your point about the XLO test cd, which I then had a follow up with you where you stated (paraphrasing) it's the "in phase followed by out of phase" track which is used (diffusion), I'm of the opinion that any purpose built cd with these types of tracks could be used effectively, correct?

For instance, in my case I use/have this one https://www.cduniverse.com/search/xx/music/pid/1526639/a/denon+audio+technical+cd.htm&frm=www.cd...

Track 2 has in/out phase.

Your opinion is appreciated. Thanks.

Re the OPs addendum, Jim Smith's book Get Better Sound might prove invaluable...
And the XLO test CD...

The BIG advantage to the XLO Test CD OUT OF PHASE TRACK is that it’s specifically for locating the speaker positions and is explained as you go along by the guy on the track as well in the booklet. It’s not obvious how to use the OUT OF PHASE TRACK so I can’t recommend a generic out of phase track unless that particular CD also EXPLAINS how to use the track for setting up speakers. If it does, I’m down. On the other hand I just explained how to use an OUT OF PHASE TRACK so you might be good to go. The IN PHASE Track is used to determine if the system is actually in correct phase/polarity only. The OUT OF PHASE track is for speaker placement.

The Denon CD does not explain (verbally or documentation) how to use the out of phase track. So your point is well taken. 

Six Feet apart center to center 
and 8 Feet listening position