Yes, I know that experiment. He did more experiments with extra speakers which I've linked here before:
Surround stereo system
He uses a processor to generate the ambient channels. I just mix and match my own signal.
The Watson seemed to start as a sort of cross talk elimination but got another function in the end. I doubt it's still in use.
I tried pointing my ambient channels up, like Linkwitz does in the link I posted, I actually build them with that kind of placement in mind. The ceiling reflection got in the way though. It was way too strong. I settled on aiming them outwards. Creating a diffuse, distant sound.
The key why this Haas kicker works is how we perceive room sounds in daily life (and the way we are trained to ignore most of it).
I've read Toole's work and interpretation and I don't think that's the same as what we talk about here. His rooms are infinite better than my room too!
I've read somewhere he experimented with Haas Kickers in an ambient space and dismissed the idea.
I have no idea what he used or tried though, but eventually Harman made Logic 7. Wasn't David Griesinger involved there at the basics which led to Logic 7? Did you see the link Jim put up?
http://www.davidgriesinger.com/paris_talk.pdf (page 8 resembles what I have, it actually works in more than one seat but the sweet spot is best, even my 9 year old kid knows that very well! No way I get to sit there with movies anymore

. Luckily I kept an eye on the sound in the off axis seats)
I guess I remembered it right. From:
Harman Kardon Innovation - Logic 7 Processing
Logic 7 is a more advanced steering mechanism than Pro Logic and a (pretty strong) competitor to Pro Logic IIx I guess. But even those are not using exactly the same ideas as the original Haas kicker. I wouldn't know how they fare though. I know Logic 7 has a pretty good reputation, even for 2 channel music while others, like Neo:6 and Pro Logic IIx seem to disappoint.
For me, after trying this ambient stuff it has become a permanent addition to my setup. I have used it with movies too, with a down-mix to 2 channels. Worked very well but after taking an hour of my time recently, I could convert my setup to use 4.0, out of a 5.1 signal as I still don't have a center or sub(s).
Even though it's easy enough to try, you've got to work with the room. The level of early reflections needs to be down sufficiently (20 dB+). The signal of the ambient channels needs to be diffuse but smooth in frequency response. All in all it takes work to get the most out of it. I'm sold, I'm only playing with reverb due to what I remember reading from David Griesinger.
It's sole goal: make me forget my room and enjoy music! Works very well for that, as you can read in the review I posted from Jan Fekkes (link in the first post of this thread). A more believable experience is what we are after right?