Waow, thank you for all these details.
I knew about your amazing job with LD audio archive, but not about this one!
Basically, the surround channels are decoded 3dB too loud. This can cause clipping in the audio during louder portions, but I have been able to correct this using de-clip in Izotope RX.
Isn’t that linked to the fact that in theatrical DTS, the LFE is added to each of the surround channels, and need to be filtered with a steep lowpass at 80 Hz ? Maybe the foobar2000 APT-X100 decoder doesn’t treat this particularity ? Basically, you shouldn’t have any sound below 80 Hz in the surround channels after having filtered the LFE signal.