Very impressive looking cost-no-object system.Might I offer one suggestion:
The basshorn is way too small to give true horn loading down to anything approaching 25 Hz. It will be in effect a direct radiator at that frequency, and will no doubt have to be equalized. At very low frequencies, the bass horn itself is just decoration.
What if you got rid of the basshorn cabinet altogether, and installed a side- or rear-firing direct radiator subwoofer in the space underneath that big round horn? In my opinion this would make a more visually elegant system, probably without little or no performance compromise.
You could actually improve in-room low frequency performance by redesigning the base (pedestal) for the two smaller horns to incorporate a second subwoofer, so that you'd have two physically separated low frequency sources per channel. I think there's definite merit in having multiple low frequency sources in a room, and so do several researchers. See Todd Welti's AES papers, "How many subwoofers are enough" and "In-room low frequency optimization", for instance.
That's how I would do it.
Very best of luck in bringing your vision to life!
Duke