The original Warner VC1 Blu has two 5.1 tracks, one is Tru-HD with 640kbs core and the other is 448kbs. In one of my times renting that older Blu, I recall the Tru-HD and 448kbs 5.1 tracks sounding completely different from each other. The Tru-HD track clearly had some separation and expanded ambiance going on in the Front L/R and Rear L/R channels, possibly some added/changed sounds in addition to prominent LFE. I think this mix was used on the Deluxe Edition DVD and sounded similar to the 7.1/Atmos mix on the UHD. The 448kbs track lacked base in the LFE channel and the rear surrounds were fed dual mono, but was overall louder and better balanced than the Tru-HD track. This track was probably discrete presentation of the 4.0 LRCS master mix and I think the very first R1 DVD release also contained this exact track too.