To comment further on the initial question, I guess what I would do is figure out how much space I have, whether I could use corners, and generally figure out what was more important to me - efficiency/speed, or extension.

If bass depth and reasonable cabinet size are high priorities, the Lamda either Pi aligned or with PR's (per the post above) might be the best solution. If efficiency and integration is key, and the corners are usable, a Pi corner horn with the JBL's could be a good option. Or maybe the "chopped" 10Pi variant if the corners aren't great. It would be a good idea to try both drivers in a simple Pi aligned box to try and figure out which one worked for the space and intended top horn the best (mono would give a reasonable indication).

Another (possibly brave) option might be to sell the lamda's and JBL's and make some sort of horn/reflex hybrid cabinet using the new 'BD15' high efficiency 15" that Bert has designed specifically for use with the Oris - there is a discussion going on about this on the BD-design forum right now.