Welcome,

When possible, you should put 3 identical speakers as a front sound stage, there is simply no better match than that. A vertical speaker as a center will also give you a much better off axis response than a horizontal one. People settle for horizontal speakers because in most cases it is impossible to put a vertical one. I your case you should definitely go with a 3rd M80. For once the salesman was right wink

Bruno
M80s/VP180/QS8s/EP600/AVR-890
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"The problem is choice..."