Without all the drama and detail of the previous, here is a design using the 10" Advent woofer in the same (Advent) box. Directivity will be pretty much the same (since it uses the same waveguide), crossover is at 1200Hz. The woofer has less breakup (more cone damping), a little less efficiency. Wants to aim a little more upward (about 11degrees), but otherwise pretty similar.
Would this crossover work with the SEOS10? The SEOS12 is a bit too large for the OLA, but a 1200hz crossover point seems to be pushing the lower limits for the SEOS10.