I have the Pi7 Corner horns and I wouldn't use a corner horn as a sub if it's being used for a surround system.

From what I know of surround sound the bass is not supposed to be directional. A rumble of a tank or herd of horses rumbles, but is supposed to give you the feeling you are IN the picture. One cornerhorn would be too identifiable for where the rumble was coming from. As per Waynes explanations the horn is the walls, ceiling, and floor with the corner horns. I expect with only one horn one side of the room would be loud and the other sort of void. Would this be true Wayne?

Pi 7's make very serious amounts of bass / treble with absolutely no effort at all so from a technical point of view you would get a lot of sound. Listening to these speakers last night (not even at high volume) it came to mind that the bass was more like atmospheric pressure changing than listening to music. If you've ever heard them, you'll understand.

Good luck with putting your system together.

Grant Marshall.