Question For Those That Watch Movies/TV Through Your Two Channel System

Do you leave your Preamp/Integrated in stereo mode or switch to Mono?
Does the dialog lose the clarity that you usually get with a center channel
speaker? 

The reason I ask is because I gifted my son a Node 2i and we connected it
to his entry level Denon AV receiver. He has 3 Mirage speakers LCR, no 
surrounds. Obviously, an Integrated Amp would result in better two channel
sound, but would it be detrimental to watching BluRay movies.

He has a turntable setup in another room with Yamaha, Rega and Harbeth,
but he wanted the Node 2i in the main family room where it would get the most
use.