I think one question you should ask yourself is what do the owners themselves have? Amie/Ian have QS8s for surrounds and since they are the owners cost is not a problem. If they wanted, it wouldnt be a problem for them get 7 M80s but they don't. Im sure Alan can also provide a much better explanation on which way to go.

Correct me if I'm wrong but wouldn't using a direct radiating speaker make the sweet spot much smaller than a quadpolar surrounds?