I dunno what the numbers really are in practice; but when we all went from Pro Logic to D-D(and DTS) we also went from limited frequency inputs for the surrounds, to full range.

I do know that my M3s out back put out some pretty low stuff when asked to do so.

Check out some other forums; some folks are even using subs in back to augment their surrounds!

......now if Axiom would consider some QS10s with 6.5"s.....