Interesting, thanks Guy for posting.
Let analyze what was done in there. It looks like well-thought, time-aligned, looks like multi-amped configuration. BTW, how the filters were implemented and what (slope/order) filters were?
To my knowledge it is the only installation that I heard about where Vitavox S2 works together with RCA 1428. It would be interesting to know how RCA driver do against S2 in the sub 1000Hz range. RCA shall go lower theoretically but I more interested to hear about sonic aspects.
A few warning comments. For Vitavox S2 to use Tractrix 600Hz with 1.5KHz filter is a bit too close in my view unless you stay with second order filter. The bass section in the middle are begging to be positioned on right and left side of the horns.
Generally if the system was put together din a day before then it might be a bit raw. Those like multi-amped horns need some time to settle down, not the horns themselves but the listener how need develop some grip of what they are hearing. As they do they might do some fine-tuning of such a playback, like roiling the tubes in amps, fine adjust the crossovers, fine tune the out of individual channels and etc…
On the separate note, did you detect that the reflection from the large window behind affects the Sound you get? This is some kind of parabolic window, right, so does it work like some kind of acoustic focusing devise?
"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche