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Question: B&W M1s / 685 / 686 speakers

Hi, I have tested some B&W M1s with a Denon 2311. Given I'll be playing music as well as home cinema I'm tempted to upgrade the two front side M1s for something like the 686 or 685. Heard mixed things about 685 / 686, any thoughts? I'm somewhat concerned about having the same technology in the front three speakers so that voice sounds good across the three. Any insights from the pros would be greatly appreciated! Also any thoughts on whether the 2311 is the right spec amp to pair up with those speakers would be ideal. Thanks v much.