1. Is there at least six feet of unobstructed wall space from the apex of each corner?
2. Will you be stitting behind where the forward axes cross?
If the answer to both of these quenstions is yes, then constant directivity cornerhorns are your best option.
Closed windows and bookshelves are OK, as are small furniture items and things like that. It is preferred that the walls be completely unobstructed and smooth, but those small deviations aren't deal-breakers. Open windows, doors and entryways are. If the window is open, it disrupts the expansion.
The midrange driver is the Eminence Delta 10A. It's the 8Ω version. You can probably source all the parts locally except for the crossovers and waveguides. That will keep your shipping costs down.