Deadfan 23,
I agree that the DI's would be plenty of speaker for your room. Now as to which one would please you best--tough call.
You might be very wise to await Terry London's review of the Ulfbrecht if that is in your budget. Will it sound 4x as good as the DI's? No, but it certainly ought to do some things better given the cost difference. More effortless, even greater clarity, deeper soundstage--we shall see. But I do believe that the DI's will remain in the sweet spot on the performance/price curve of the Tekton line.
As for the 1812's, I don't have a clue. I have to believe they would sound different from the above two speakers as the driver configurations would have different appearing wave launches and dispersion patterns. One question I might have with the 1812's--can the woofer be placed against the front wall and the the other two arrays be brought out into the room to optimize bass extension (which probably is not a priority for you) while maintaining a great sound stage? I only bring this up because in my dedicated room I have the DI's 6 feet from the front wall. They sound great--but they do not go down to 20hz. Probably 32 would be my guess.
So far, Eric is the only one who has heard all three, so I'd be asking him very focused questions on the things that are important to you in a speaker. Good luck and keep us posted on what you find out.