The in wall subs require making a big hole in your wall. If your wife freaked out over the little EP175, what will she think when (say) you cut a 23"x13"x4" hole in a wall? Yes when finished it can look fairly neat, but it will be a big mess beforehand.
I hate to suggest a non-Axiom solution but here are three more:
(1) Hide sub in "plain sight" as an end table. Typically this requires a down-firing sub with a finished top, like the Hsu VTF-3R:
VTF-3R MkII Put a lamp or vase on top and few people will know the difference.
Alternatively maybe Axiom's custom finish shop could build an Axiom sub to a similar look.
(2) Use a small cylinder sub laid horizontally behind a couch. Bass frequencies are non directional so physical placement is less restricted. Out of sight, out of mind.
(3) Get the smallest decent sub possible and hope for the best ("look dear, it's only this big"). The Velodyne HGS-10X is an 11" cube:
Velodyne HGS-10X 
