Quote Originally Posted by PeruvianSkies
My problem with taking a 5.1 mixed film and watching it in 2.0 is that there is information loss....no doubt about it. You can't possibly watch it without noticing that there is something missing, no matter how great of a 2-channel setup you have. Where is the rest of that infromation going? If it's discrete 5.1 sound than it is getting compressed down into 2 channels or information is just getting lost. Now if the movie contains an option for switching over to 2.0 channels than that's fine with me, but anymore it's usually just 5.1.
The only actual information loss that occurs during a default 5.1-to-two-channel mixdown is the LFE track, which gets jettisoned in the process. Otherwise, the mixdowns occur at predefined ratios, with the center and surround channels getting folded into the R and L main channels at about 70.7% of their original levels. The information from those channels is still present, but blended into the main channels at a lower level.

Problem with this process is that it does not account for the actual signal content getting sent into the center and surround channels. Soundtracks that mix a lot of the ambient cues into all five channels simultaneously will actually boost those sound effects and drown out the other sound elements that are more anchored into the front soundstage.

If you want to preserve the LFE track or have the mixdowns done somewhat differently than the default, then you'll need to use the virtual surround function on your receiver/processor by switching the channels off in the setup menu.