I think it would good to know what kind of speakers you have or did I miss that? Are they front firing for example?Dipoles? You have 19' depth on the short wall so I would definitely agree the short wall should the wall behind your speakers- experiment at any rate- with your speakers at an equidistant or equilateral triangle with your listening position. I guess that's a no brainer.
For ceiling reinforcement think about those bed liners that they use in hospitals as they are thick foam with pretty deep pockets so they don't have an even surface. Medical supply stores are the place to get them but it may run you quite a lot. You could probably drop a few of the over the metal beams or lay them in above your tiles in front of your speakers and listening position. I don't have any experience with this, I'm just thinking out loud. What I do have experience with is removing the early reflection of sound waveforms from your speaker faces if you listen with boxes with surface mounted tweeters.
Less you think this isn't offensive look no further than Vandersteen or Green Mountain Audio models and you can see from modern design that waveform behavior is pretty dominant. I can tell you that taking your enclosures out of the equation will open up your space to what sounds to me to be unbound from my room boundaries depending on the miking and mixing of a recording and the images appear more lifelike, rounder and truer, without the artifice of baffle reinforcement. I love the way they just appear in front of me more dimensionally and substantially. I'm steady trippin! This is real science in the service of aesthetics.
That's the reason I manufacture them for traditional box speaker owners like myself. I got a website if you would care to learn more and read a few comments and a review. Go to "Industry" circle and there I'll be.
Anyway, keep posting your progress, my brother. Who wouldn't like to be able to do what you can.
