On the M3's and M3ow's Axiom will put in inserts so you can mount them on FMBs or FMCBs but you need to request them up front. With the M5's & M5ow's I assume you can do the same ...
All the bookshelves come standard with a single insert in the back which I think is for a FMB. But I'd verify it's use with Axiom before using it. Especially the M5 given its weight (don't want to find your M5 on the floor because the insert worked its way though the ply).
I'd imagine that Axiom would do this also if you want to invert your speaker. I'm going to ask if inverting it is ok sound wise. The only other problem I can think of is that dust might enter the ports since they are facing up. That might be solved with some AT material.
Another way to approach this is by putting some screws in the back of the on-wall and figuring out some sort of bracket.
Note: that axiom will put in binding posts on the M3ow's when inserts are requested for FMBs and you loose the T bracket. It might be possible to keep the T if you pass on the binding posts ... another question for Axiom. Then you can just use the T as a connector and still have the option of mounting it the other way. I personally would not use the T if flush mounting to the ceiling. If I decide to do that I'll design a bracket ...
