One bit of information to add about qsound. Madonna, Sting, and I believe Roger Waters has used qsound in the mixing process on an album

Right. I'm quite familiar with those examples and with the Qsound 3D spatial processing, which is a different thing than what was being demonstrated at the front page of the web site you linked.

I remember getting Sting's "The Soul Cages" and seeing the note on the sleeve about how it had been processed with Qsound. I also remember, around that time, seeing an interview with Michael Penn about how he liked using Qsound in his production. In listening to the Sting album, I do notice a certain presence and sparkle to the production that wasn't there on the prior albums, so it certainly was doing something good.

One thing to keep in mind is that Qsound is supposed to allow the artist to give each instrument a more easily-detectable "location" in the stereo soundstage. For instance, you are supposed to be able to hear the guitar coming from "over there" and the bass coming from "over there" instead of it being just a vague stereo pan. Also, it's supposed to be able to widen the soundstage so that it appears to be wider than the physical distance between the speakers.

But for all of those things to be possible, the work has to be done ahead of time, in the mixing studio. You can't apply Qsound after the fact and have it extract the instrument locations from nothing. Hence, my statement that this processing should not be applied at playback time. The fact that Sting and Madonna (heck, lots of artists) use their technology in the recording studio only reinforces my statement.

What you linked at that web page was something different, though. It wasn't just 3D spatial processing. It was also a combination of playback-time EQ and echo effects.

Something else I didn't mention in my last post, and I just thought of it. I wouldn't be surprised if they were also applying some per-frequency phase correction, in the same way that the BBE devices do. Now, I've heard the BBE stuff in action, and I can understand how something like that can be useful at playback time. But again, it seemed that the demo soundbite at the page you linked was doing much more than this, and it was adding a lot of uneccesary echo to the recording.