I have met you in the NYC Audio Rave in CT, at Hogg's. The idea of making an OB with the B200s as well as a companion sealed sub box to augument the bass is more than intriguing! The box cosmetics would need not to be too great if you hide it behind the OB itself. What is intriguing about this possible design is the hope of getting some tangible low frequencies from a fullrange set up.
I have heard several fullrange versions of the Fostex's, sealed or hornloaded and although many of them do extremely well in the HF and the midrange, I was sorely disappointed along with other people at the lack of "heft" in the low end.
Strangely enough, most of the Fostex versions did go down to around low 40s and even to mid 30s, but could not compete with BR 2 way minimonitors that were rated to around 50hz. I do not know why of this discrepancy in perceived heft or low end.
The only FR single driver that was able to quench my thirst to LF was a pair of F200As in a rather large, almost 100lbs cabinets that were made by Bob Brines called FTA-2000s.
The OB with the augumented BR low frequency box has great, I mean great potential, if it is able to produce heft in the lows.
PS: Doesn't this design sound very similar to the Dick Olsher speaker, as well as that German outfit that sells a similar set for around 2.5K?
Great potential here....as long as the price is not prohibitive. Care nary around looks, more about the sound.