>If I have a large screen (100"+), will I need a dedicated center channel to hear dialog well??
No.
It may even be more intelligible without a center channel where you don't have an acoustically transparent screen which forces center channel placement above or below the screen where it gets a lower midrange boost due to the boundary proximity.
I turned off my mis-matched center channel in my main system and haven't gotten arround to building appropriate center channels for either main or bedroom systems (where it's on higher on my agenda since I sit off-center in bed which produces image shift, although that does not interfere with intelligibility).
>I am concerned about blu-rays needing to downmix from 5 to 2 channels and with such a big screen and separation of my mains, will two channels just make the dialog more diffuse??
Not with good speakers and setup.
No.
It may even be more intelligible without a center channel where you don't have an acoustically transparent screen which forces center channel placement above or below the screen where it gets a lower midrange boost due to the boundary proximity.
I turned off my mis-matched center channel in my main system and haven't gotten arround to building appropriate center channels for either main or bedroom systems (where it's on higher on my agenda since I sit off-center in bed which produces image shift, although that does not interfere with intelligibility).
>I am concerned about blu-rays needing to downmix from 5 to 2 channels and with such a big screen and separation of my mains, will two channels just make the dialog more diffuse??
Not with good speakers and setup.