Marlboro,I made a 4 stack with the Fostex 3" driver. The price is better than the Jordan. The low extension is not there though. The sound was good , but I was listening in the "far field" area. I ended up putting in a coil to reduce the lows at 300hz. This made the sound clearer.
The center spacing may not be as much of an issue for a full range driver. The highs come from the entire cone. Not just the center. I think that the highs move out from the center as a wave along the cone surface. I wonder if this would help reduce the effective center spacing.
-Linc