I did a search for "obx" (thread titles only) in the mazdaspeed 3 main section (and the forced induction and engine sections) and came up with zero results. When I searched for "obx manifold" (titles and posts) it came up with a bunch of junk and I wasn't able to find anything after searching through several long threads about manifolds.
I always search first, because I hate waiting for an answer.
Anyway, I don't see much need for a twin scroll turbo on a FWD... some lag (provided by a huge turbo) usually helps maintain traction when drag racing in a FWD, and a smaller turbo for street driving doesn't need a twin scroll design to spool up fast. That manifold might be more useful on a CX7 or Mazdaspeed6. I just figured I'd see if anyone was using it on a speed3.