My opinion in the end was to trust my ears and my gut. I can't help but feel that the official crossover spec is redundant unless you happen to have the same equipment, correctly positioned in a space of the same size and shape, and with the same calibration as an actual cinema. In the end, after resigning myself to the fact that it just never sounded right, I used my ears and some reasoning.

At this point I've tinkered with it so many times that I cannot remember exactly what I did in the end to get the final result. I took hairy_hen's advice and processed the surrounds and LFE in Ozone to get a better crossover, and adjusted the low-pass cut-off to create a cleaner, and more relevant, LFE channel because it seemed too active before.

I also tried the foobar plugin to see what it ouput. In my tests it produced decoding errors in the surrounds and LFE's in short bursts, and in several places; sound that most certainly isn't present on the discs. I don't know whether it was a configuration issue on my end, but it did it with each AUD file that was fed to it, so in the end I stuck with the files I decoded three years ago using the Winamp plugin.