It would be fine with some damping on the speakers. I think Axiom sends out silicone stickies with the bookshelves.

Try to keep the faces of the speakers flush with the sub faces to minimize reflections and diffractions.

A bigger problem might be location of the subs. If the speakers are being placed in a corner (of course that wouldn't be you), the subs may go BOOM! I've found a third of the wall away from a corner and away from the wall works well for subs.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated