I have two PB13-Ultras and two SB12's -- I'm using the Ultras
From what I've read, I'd recommend the SVS MTS line of speakers -- not cheap, but they'll do what you describe you want. If you can't get clarity out of an AirCirc tweeter, it's not in the recording.
I concur with others that you HAVE to do some treatments. Even detailed EQ isn't going to stop nearfield reflections from blurring your soundfield.
Easy stuff:
If your floor is not carpet, get carpet or large rugs.
Put up a traverse rod over that glass and hang thick drapes.
Hard stuff:
My guess is that your biggest problem is your loft ceiling. Ceiling treatments are expensive and for the most part permanent (a problem if you are renting). One less expensive temporary solution is to use heavy insulated drapery material supported by 1x3's screwed through the drapery material into studs in the ceiling. The drapery material hangs down in U s between the 1x3s. At a minimum, you'll need to treat the ceiling immediately over your listening position, as well as the first reflection point from your speakers (a strip about halfway to your speakers).
Since you have an SMS-1, try this: Put your Ultra in 10Hz mode (for lowest group delay not extention). Now use your SMS-1 to make a 'curve' that is as flat as you can get it above 40 Hz, and gradual straight line rolloff below 40 Hz. It's really two straight lines intersecting at 40Hz. I came up with this by ear listening to classical instruments, but I've subsequntly read that this kind of EQ curve often works well in mid-sized rooms.