mceljo
for simplicity, let's say center channel is dialog.
I understand your method, HOWEVER,
that does not solve 5.1 movies/music videos, streaming. 5.1 has DEDICATED center channel content (mono) as well as dedicated L/R rear/sub out. The 5.1 center channel content does not exist in the L or R channels, thus, for 5.1 content you NEED a center channel speaker.
When you tell your AVR to use 2 channel/stereo mode (as I often do), it then reassigns the mono center channel content to the L and R channels (dual mono) so a phantom center image exists as it does with our 2 channel music systems. The L and R are also making phantom imaging (a bit left/a bit right/center) like 2 channel stereo does. The rear and sub out are also moved to the front L and R, directional cues lost, but content present.