You mean they are actually decoding the 6 channels from the MLP DVD-A track, then down mixing to 2 channels and then doing an additional decoding/up-mix? Bizzare! I wonder why they would do that? While MLP has down mixing built in, some discs, like Queen's Night At The Opera doesn't have the MLP downmix parameters set correctly - the 2 channel downmix is only the front L/R channels. You have to listen to the PCM track if you want the 'full' recording - and since it's not a proper downmix, it isn't compatible with a decoder like Circle Surround, Neural or PL-II. And many DTS CD's are flagged not to downmix to a Lt/Rt matrix compatible signal at all.
I haven't bought a new car in years, so I have to ask about you saying that you auditioned the "THX2" in a Lincoln - is that just a model number or is it really the THX company, uh, "certifying" car audio systems? If so, I weep for the THX program and what it originally stood for.
I had a 1987 Chrysler New Yorker that had an Infiniti II system that was wonderful - I ended up putting a Fosgate Gavotte in it - the New Yorker's Infiniti system already had a center channel in place, so adding the Fosgate was a minor issue, and it made a MAJOR difference in the car - all cars should have center channels, either discrete or logic-derived - I always wanted to put one of my Fosgate Tate II 101A's in the New Yorker, but I never got up the nerve; I was afraid something bad would happen to it - and the Fosgate Tate can't be replaced as easily as a car can! My 1992 Chrysler New Yorker/Fifth Avenue had a Sony DAT deck in it - I LOVED the DAT format and imported prerecorded DAT's from Japan like crazy. I still use my Sony DTC-700 DAT recorder - unlike many people I haven't had problems with tapes mis-tracking over time or dropouts, etc... When MiniDisc came out I went totally gaga for it. I always thought DTS Digital Surround or Dolby AC-3 would be a good 'fit' for MiniDisc - allowing you to have a very small, well-protected and portable surround-sound format for the car. (BTW, was Philips DCC format ever made as a car unit? I don't recall ever seeing or hearing of one - I have one 'demo' DCC tape that says "for display only, not to final spec". How about an Elcaset for the car??? That's a format I sadly never got to try - I was only 10 when it was introduced.)