Wolf: You make some good points and address something I didn't mention. Although the total open space is large, the speakers would have a solid wall behind them (2-4 feet away) and the Prelude Pluses have a rear-firing port. Also, I generally listen from around 6-9 feet away, so the speakers don't have to crank too hard for me to hear them well.
Also, sub integration has not been a problem for me either. I have a pair of Mirage MM8s, which were designed to blend well with satellites and small towers. They are sealed enclosures with 380/1200 watts rms/peak driving an 8" aluminum cone with linear high excursion surround, and augmented by two matching passive radiators. They don't go all that low (about 36 Hz), but they fill in where small speakers start rolling off and they are very fast and have continuously variable controls for 0-180 deg. phase, volume, and crossover frequency ranging from 50-250 Hz. They add just the right oomph for speakers whose bass doesn't quite fill out the space.
Mapman: My current speakers are Mirage OM-15s, which are omnidirectional floorstanders. My experience with their uniform tonal balance and soundstage throughout the room matches yours. Since Klipsch has gutted Mirage, discontinued the brand and no longer makes replacement parts I figured it's time to move on.
I found that if a speaker has excellent and uniform dispersion and in-room power response, the soundfield is similar enough to an omni that I could get along with it well.
The Prelude Pluses, with their very small woofers, should not have a room suckout when handing off to the tweeters. The narrow baffles should provide pinpoint diffraction-free dispersion, and the rear-firing port should balance out the bottom end. Add the subs and they should do OK in my large space, especially if I'm listening within 6-9 feet most of the time.
I'm also considering the Odyssey Lorelei, Ascend Sierra Tower, Salk SoundTower, Gallo Classico 3 or 4, and Magnepan 1.7s. The Magnepans obviously have different placement issues, but have such an addictive see-through sound. If anybody knows of a dynamic tower that approaches that 3-dimensional transparency free of boxy resonances, let me know.
