Sorry to boost a very old thread, but we’re still trying to find the original theatrical mix. I am not an expert, but here is what I have deducted so far. It seems that originally Leon was released in 4-channel Dobly Stereo and 8-channel SDDS (the so-called theatrical version), which we can clearly see from the titles on the print:
https://imgur.com/a/hqHF4Dn
Then Besson decided to re-release the longer version for the bored office workers in the summer of 1996, and it seems that the only audio they had on that release was just Dolby Stereo, which we can see here:
https://imgur.com/a/r2Z39XL
Some people mention that the theatrical version was released with DTS as well, but we still need a confirmation that this was the case. DTS is never mentioned in the titles of the print.
Also, if you look at the 35mm film cell strips they sell on eBay or whatever, you don’t see DTS time code on them, only optical stereo track:
https://imgur.com/a/aMRq6El
This however might be the film cell strip from the longer cut (no SDDS track on it either) and the DTS still could be found on the theatrical cut print.
Be as it may, one thing for sure, the 4-channel Dolby Stereo found on the LD’s, DVD’s and, probably, on the Optimum UK Blu-ray in the lossless form, must be the theatrical surround mix.
However, I’d be happy if someone with more expertise could comment on this.