Revel C583 or C783 or different brand?

Hello all.  I picked up a pair of F228be - L/R, C426be - C and two days ago a B112v2 - Sub.  Powering these is an Anthem MRX740.  I have to use in-ceiling speakers because my home is an open floor plan.  

1.  Are the C783 worth the extra money?

2. Is the Revel Steel Back box required?

3. Should I buy another set of either for Atmos or does the in ceiling rears negate being able to utilize Atmos?

4. Is there a better alternative, brand wise, ie, Focal? JBL, Martinlogan, ect... or should I stick with the Revels?

Appreciate any advice, thank you.