I’m not an audiophile, but I found the sound effects for the 5.1 to be amazing while the music cues and dialogue were sometimes too soft. Is that fair or am I crazy?
I’m guessing that’s the stereo mixdown h_h was warning about. 5.1 mixes mixed down to 2.0/2.1 get softer than if they’re played back on a native surround system. I think there’s even some cases where you could hear this on a surround system, if your TV doesn’t do 5.1 passthru on optical, so it mixes down to stereo, then your receiver mixes it back up again.
But basically, the advice holds: if you’ve got a stereo system, listen to the stereo mix. It’ll be clearer due to lack of mixdown.