Speaker placement

Can’t help with a high ceiling as I have never had to deal with it. The kicker is it is a fixed distance. Hopefully you don’t have cubed dimensions. 

To get a little more scientific. you can look at 1/4 wave lengths. 1/4 length cancel because by the time it bounces off the walls and comes back it is a 1/2 length out of phase with the driver. 

The tricky part is the front wall, back wall, side wall and ceiling all count. So it is best to have different distances between all of these so the cancellations blend together to fill the holes. Worst case it have the side wall and back wall be the same distance as in both 4’. Get ready for a giant hole in the sound of this is the case. 

The short version is all walls between between 3’ and 6’.6” should be avoided for bass. Closer than 3’ is actually better than between 3’ and 6.6”’. After 6.6 the bass lumps tend to go away and the speaker soundstage opens up. But closer than 3’ and your mids get muddy. 
If you can’t get your mains 7’ off the walls one of the best solutions is to use subs so you can cross them over and tuck them less than 3’ off the walls and pull your mains out 4-5’. This will fix a null issue as you can place different frequency drivers in different places. 
Chart so you can calculate it for yourself. http://www.soundoctor.com/freq.htm

Video for the reading impaired myself included lol. https://youtu.be/T10_MLGOBfc

SPL readings in the corners are perhaps useful if you're going to be hanging out in the corner. Note that most rooms have their own sound and hey...embrace it...the world is full of rooms, and much of what is "music" is performed in them. I like room sound, although I don't like bad room sound and furnish my listening rooms with human related items...books, CDs, LPs (and a few singles), furniture, myself, others (rarely), guitar cases...you know what I mean.

Crap the dog erased my response.. No kidding..

WOW that is a big open room.. you did a LOT more treatment than I would have EVER done.. you did a GREAT job there..

2 channel right? Turn off everything BUT the mains, and pull them out from the wall. 4-5 feet to begin with.

Set the cut points for the mains, 50hz is going to be a push in that BIG room.

Get the center phantom the way you like. Nearfield is gonna have to work, kind of a nearfield. The toe is going to be very critical. Get your phone turn on a SPL app and make sure the the DB level is the same left to right at the seated position. 50, 300, 700 1k 5k, 8k. You know the drill tone burst readings..

How do you adjust that? One speaker one inch further back and 1/16 " MORE toe in will do a LOT for db levels.. 1/2 inch at a time, BACK and reset the toe. To get real techy top to bottom too, TIP it forward tip it back.. Even left to right can change a lot of issues an EQ can't.. Mechanical EQ first, then gear EQ..

NOW

3-4 small 8-10’ IB subs.. NO PORTS. It would be nice if the plates had variable phase up to 180, delays an PEQ would be capital..

Turn them on 2 at 50hz 2 at 40hz, (I’m close with those high ceilings).
The steeper the ramp the better too, 12-24 db 2nd to 4th order XO.
A 6db first order is a NO NO in that room.. Set the plates at the 1200 position (GAIN)

Your going to have issues..
ALL PEQ (DSP) and main placement.

NOW

Coherence and width of soundstage in a NF,

PUSH the speakers BACK toward the back wall 1/2 inch at a time, keeping the TOE in, the same as before you turned on the subs.. Use blue or green tape to keep it straight use a square to keep your toe.. (Roofing square is a great tool also). REMEMBER your DB adjustment left to right.. Keep that number correct (+ 1/2 or 1 inch and the toe setting)

The further back you go the better UNTIL it just starts to get muddy and turning DOWN the gain to 11:00 doesn’t fix it. THEN pull the speaker back 1/2 the distance from the LAST movement.. as little as 1/4 of an inch..

11:00 to 1:00 on the sub gain depends on the music. Classic to Hip Hop..

That’s it.. But just so you know I like ear buds.. LOL Just kidding..

The corner SPL were for wolf, he spent a lot of time there as a kid..
I hadn’t seen the room Mr smarty pants.. LOL It’s a doozie!!

Regards

Thank you everyone again for all of the fantastic help with getting my room dialed in. I’m looking forward to making it the best it can be.