I have a somewhat similar situation in that I wanted to put a pair of M3's on a screen porch. The porch has a peaked roof so I plan to mount them up on a beam so that I could completely avoid any rain getting on them. I live in NH where we have very extreme temperatures in winter.

I sent my question to Axiom and Alan answered back that they would do fine in that environment. He indicated that there is an Axiom employee that uses a set in his unheated garage and that despite the very cold Canadian winters (they probably have NH beat!) the alum. and titantium drivers aren't affected.

So...ordered my M3's from the factory outlet last week and am anxiously awaiting their arrival!

In your case the big issue is going to be the precipitation which would probably ruin the cabinets. The outdoor speakers I've seen are sealed designs so the port on the back of the M3's would be a big problem.

How about using banana connections and just pulling the M3's out when you are actually outside? Would be a pain but at least you would have great sound at a reasonable price.