I've got the SEOS18/TD15M/BA750 parts in my possession.
I'll be going for max. sound quality for a 90% music/10% movies system. I initially wanted to go with a ported design, ~6 cu ft with a tuning freq. around 35hz. I'd start to bring the subs in @ F3/ 50hz. Presently, my latest plan is for a 3 cu ft sealed design. Hmm.... would I get better SQ with a sealed box? From what I've heard, a sealed enclosure would be easier to integrate with my subs. A 3 cu ft box would be easier to make stiff, dead and would not dominate my living room like a 6 ft3 box.
I plan to make the box very dead using a constrained layer between two sheets of ~9/16" void free 11 layer ply. Here's a very interesting build thread that has some box construction ideas which I may use.http://www.diyaudio.com/forums/multi-way/218437-3-way-active-time-aligned-constrained-layer-construction.html
I plan to go with an active crossover. After the dust clears, I don't think it would be much cheaper to use a passive crossover, besides I don't have any experience designing passive crossovers. Digital amps aren't that expensive nowadays and I already have a nice tube amp for the CD. The data shows that the BA750 is fairly flat to 650hz, so I could then pass it to the TD15M. It would be great if a reasonably priced beryllium diaphragm could be found for the BA 750. Although this is an attempt at a fairly high end design, I do have to keep an eye on the costs.
I'd like the speakers to be a freestanding box design with the back side corners cut ~3" @45 degrees. The SEOS18 would sit on top and partially enclosed in its own box. The good thing about this arrangement is that the bass bin would be totally separate in case I wanted to experiment with other waveguides. It would also make moving the speakers easier and separate the vibes of the woofer from the WG.
I still haven't decided exactly what I want to do, so if any of you have some suggestions or advice, it would be appreciated.