Which speakers will fill 5,000 cubic ft coherently

Pick your poison. I would go for a wide range single driver midrange. Look at the classics like Ls3-5a, original Quad, Spica TC-50, original Advent, etc. All were as simple as possible. K.I.S.S.
Time has taught us (some of us) that complexity brings with it complication.......and problems.

I'm impressed with what I've read about SP Tech. I spoke to Bob and he does not feel the location (near the front wall) or size of the room, or the fact that I have a tube OTL amp are impediments. (I know, I know, 8 ohms is better)- but I still haven't found the ideal speaker in theory, and SP Tech is getting raves. Comments?

Thinking over your problem again I think I'd be taking a look at reflections from the floor under your system.
Your high ceiling may be changing what might normally be balanced by an 8 ft ceiling.
Could you advise your flooring around your system & speakers?

jbl 4430/4435 studio monitors.

I noticed that the Coincident Total Ref has been replaced with the Pure Ref model. Quite a bit of verbage at high-endaudio web site about these...

Thank you all for your input. It is most appreciated. I am going with the SP Tech Revelations III, guided by many who have listened to them as well as the other contenders. I am especially indebted to Duke, who despite being a competitor, gave frank and honest advice. The only reason that I didn't buy the Jazz Module is one of size and likelihood that the far taller Revs would fill the room better. Furthermore, Bob Smith, the owner and designer will modify them to accomodate my awful room placement issue and will design a passive equaliser for close-to-corner placement and to reduce the demands on the Atma-Sphere for bass drive. I am taking a small risk in that the Revs may do better with biamping with ss for the LF, but will cross that bridge when I have tried the A-S amps. I have been really impressed with Bob Smith's out-of-the-box approach to tailoring his speakers to both the room and the amp and his sound reasoning for (hopefully) making this work.

Thanks for giving feedback - I would only add that it might be wise NOT to modify the SP Techs or alternatively make sure you have a kit to make them standard again...just so that you keep your resale options open and also the option to move house or change their location in your house.

Shadorne, all the changes will be incorporated in the bass equalizer, an external box, placed between the amp and preamp. It wont affect the speaker design physically. Because it will be placed in the corner, almost, Bob will utilise this fact to reduce bass demand from the amps and other technicalities that are beyond me........

My friend, I had a room similar to yours with Kharma 3.2, and I struggled for exact the same reason.

Maybe you can try the Verity Parsifals!