Why not start with 5.1 and see if that's good enough? Or if you have a newer receiver, adding WIDE or HEIGHT speakers adds more to the overall effect - so I'm told.

I believe I'll be going with the HEIGHT speakers soon. According the the people that invented it (Dolby PLIIz or Audyssey's DSX), the order of importance is WIDE followed by HEIGHT.

But in my room, WIDEs are out of the question.

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Denon 4520, EPIC80/500/VP180 Speakers