Like peter pointed out, the W series are not primarily designed for surround sound duty in the Axiom Lineup, however, that doesn't mean that they won't sound great (I just setup my father-in-law's theatre on a budget, using the M2s as surrounds).
The Axiom QS8s are Axioms top of the line surround sound speaker (designed specifically for surround sound duty).
If you have no budget limit, or other limits, I would get the QS8s, they are superior to surround duty than any other axiom speaker due to their quad polar design (4 drivers firing in different directions all in phase, creates a very "spacious" listening environment).
Regarding the mounting height, I would recommend 2-3 feet above the listeners heads, so that the whole room can hear both of the surrounds.
