Wayne has a post where he explains it all, but I can't find it.
Basically, his design uses the corner of the room as a conical horn. Other corner horn designs (Klipschorn, Jensen Imperial, etc) use more complicated horn expansions, but still use the corner of the room as the final expansion.
The last couple pages in Wayne's Pi-Align white paper show the design. Quite simple, just a ported enclosure, but rear firing, as you saw at your buddy's house.
I see the design as a hybrid between bass reflex and horn loading. Basically, an intelligent use of room geometry, provided you have the right kind of space. Because of the corner placement, you get full coverage of the entire room, and the first reflections are the opposite walls and/or ceiling.