From the MA facebook;
There is a difference, BX was very good, but they managed to improve, even better soundstage, more detail, more présence in the low frequency, and the White ash finish is astonishing, and a unique finish in this price range. Bronze 6 is the biggest improvement, very rich and more balanced low.
I am saddened they still make MTM style center tho. Monitor Audio said there isn`t enough asking for 3-way center. From the BX 5.1 review:
Off-axis, however, the BX Center suffered from one of the response-lobing effects so common among two-way horizontal designs. When listening from 20º or so to either side - about equivalent to the extreme end of the sofa in many real-world home theater spaces - the sound was noticeably changed, losing high-midrange content and thus lending a slight but detectable hollow/ dull cast to most voices. As long as my head stayed reasonably centered (rare, I admit!), though, the BX Center sounded very fine. The center-channel unit made an unusually close match with the BX2s and, when auditioned on-axis (from the center seating location), created a truly seamless "front stage."