I had the console out of my 2006 last weekend to wire up a CB radio. I
could be wroint but I'm pretty sure that that the wiring for the rear
speakers stops towards the rear of the console at which point there is
a plug into which a wiring harness from the speakers plugs into.

I asked the dealer and found out there is a speaker kit for around
$125 that includes the 2 speakers, mounting brackets, and wiring
harness that I imagine goes down to this plug.

BTW, if you're going to be taking out your console for any reason I
recommend getting a copy of the parts explosion for this area from
your Mazda dealer so you can see where all the hidden screws and clips
are.  It's not nearly as obvious as the NAs and NBs.

Jon Weinberg