The issue lies with the extended codecs used for DTS-HD, since the core DTS track is fine, if it does exist.
And my surround system was a top of the line model ten years ago. But I am finding that, since I'm watching the discs on a PS3 hooked upto my Yamaha system by Digital Optical which is only sending the core DTS codec (at a bit rate of 1.536 MB per second), and I usually watch all my stuff this way, with my TV receiving the video via HDMI. But I tried the audio from the HDMI (which, as far as I can tell my PS3 is sending the signal in PCM 2.0) and I did hear some muffling and echo of the audio, but that is usual when I play back other DVD's and Blu-Rays that only have a multi-channel track and get down converted too a 2-channel mix.
But my TV also outputs that HDMI audio signal over the digital coax (by PCM) and when I try the audio in a surround mix, that is the only time that I pick up any really audio change, or even the "tin can" effect. But that's because the signal's getting digitally mixed from a 7.1 source down to a 2.0 mix with no fine tuning.