Great review!
We have things in common. I have 3.6s, a 14’ wide room, and also used REW extensively for set up (see my All out Assault REW plot - Oh, I need a little more toe in....). Surprised about the treble as many complain their ribbons are too hot. This should be fixable.
Some ideas include: 1) more break-in time (probably not)?; 2) assume your room is fairly symmetric?; 3) Everything sounds like you’ve optimized for bass. Most likley you’ve overdamped your room. Did you damp the front wall? - should use diffusion there and damp behind the listening seat. Check RT60 up top - I’m betting it’s below .3mS. 4) You’ll get a much better center image with tweeters in, but lose that big sound stage. To me it’s a worth while tradeoff. 5) Between 5-6’ from front wall Maggie’s imaging starts to get more diffuse. Farther away is not always better. 6) The last thing I’d try is an amp change as this should be fixable with placement/treatment changes. Note: the Adcom is really nice, but it’s real strength is mid & bass. Top end is a little rolled off. Read the original Bascom King 5800 review (I have owned both the 5800 & 5802).
Thanks for the .7 comments. Sounds like a really great speaker!
Check this pdf on Acoustic Measurement Standards out, but don’t take it too seriously as it’s "ideal":
http://www.acousticfrontiers.com/20111013acoustic-measurement-standards-for-stereo-listening-rooms-p...