Why not horns?

You would use a capacitor and pentameter or fixed resistors if you can afford fostex r100t transformer attenuators even better. Some Altecs might need networks updated but most do not.The t900a has a stand you just move it forward or back to get some time alignment vertically. Very easy to do.

OM Horns

These are horns that I think I could live with some day if they sound as good as they look.

They do. In fact, many people would say they sound a lot better than they look. They were designed for OMA by Bill Woods.

A bargain at $53,000?
HELLO, earth to reviewer.
Those cost of those speakers (to me anyway) are a sure case of 'why don't I try and build my own'?

The cost is the one thing I suspect I could not live with and would be the reason "why not horns" for me in this particular case.

Also there is a lot of competition at the $53000 price point.

Also it seems that very expensive speakers in general seem to depreciate the most on the used market as well which makes them a bad investment. People with the money to afford $53000 speakers are not searching for used bargains I suspect which means the prices have to come way down into the range of mere mortals to re-sell without taking a big financial hit.