Just be aware that most (no, not all, but almost all; some OPPOs may well be exceptions) players drop the LFE channel altogether from 2-channel downmixes of x.1 audio destined for their analog outputs. Whether this low frequency info is encoded to some degree in those soundtracks that are specifically mixed as stereo mixes, I do not know. But there are very few discs with stereo-specific mixes, anyway.
AVR's and pre-pros do not drop the LFE info when downmixing for 2-channel (or any subwooferless; 7.0, 6.0, 5.0, 4.0, 3.0, or 2.0) output.
joecmess, are you absolutely certain that you are applying the exact same processing and post-processing to the material you are comparing? Granted, they are two completely different soundtracks, and they may just be that different, but I would not have expected a huge difference. Is it possible your pre-pro is applying PLII (or other processing) to the 'stereo' mix? Is it possible the multichannel mix is DTS while the stereo mix isn't? Etc.?
"All men are frauds. The only difference between them is that some admit it. I myself deny it."
Last edited by sivadselim; 03-17-2015 at 11:46 AM.