Jeff,
How well would the MG212T w/BA12-3 on top work (Kringle mentioned it & sounds interesting, if you have the right amp for the impedance) (& cut the HF on the 212, right?)?
You know I have very mixed feelings about all of the combining cabinets discussions here.
As a manufacturer you develop a product line (call it a product roadmap) so you know where your going with your offerings --- before you ever release anything. But the beauty of this forum and our participation (manufacturers in general) is that we can have such a direct conversation with a wide variety of players, users and potential users and if your listening (which we certainly do) you consider the other opinions of what you're offering.
That is really a beautiful thing.
So even your best laid product roadmaps may require revisions and alterations as you see how the real world is actually using your products.
That gets us to the discussion about combining a design like the Bass Array cab with other more traditional cabinets. I would say that with all the dozens of cabinet designs I've developed and brought to market over the years, when conceptualizing and developing the Bass Array design I felt that THIS is surely a design that best works by itself, individually or in multiples (in the case of 9 3/4 -- a stack of 6

) and could have more detrimental characteristics when combined with non similar cabinets.
I've had this discussion with so many users of the Bass Array cabinets and that combining 2 cabs goes way further in their combined output than just stacking 2 conventional 1x12 cabs.
As I see how players might want the benefits of the BA design but with a consideration to more LF output underneath it, certainly if you have a cab already and want to add the BA, you're not going to hurt anything. Are you going to get the full benefit of the BA design.....we'll that's more subjective.
I guess if you're asking for my input, I'd rather potential users of the BA cabs consider that they're about ready to embark on a "different aural experience" if I consider these cabs and with that they should consider that this is more of a transition to a new speaker system and not an enhancement to what they already have. When we sent the proto cabs out to several players of varying styles the above statement was pretty consistent.
Sorry if I'm a little long winded on this Sunday morning with this subject but I hope this provides some background into several of the questions being asked about various potential combinations. Really can't hurt anything in the long run but am I getting the full impact of what is being offered.
Thanks for listening and yes we continue to listen from our side too.