The 8-disc Blu-ray collection is missing the high-quality audio. To get the DTS-HD MA audio you have to buy the individual Special Edition Blu-ray edition of each movie. There's no point in buying the 8-disc collection. You save a little bit but miss the full enjoyment of the movies and all of the extra material.
This is also not the "complete" collection. The first two movies were released with added footage as Extended versions. These easily fit together with the shorter versions on the same disc. In fact they both versions are on one disc in the Special Edition set.
The loss in audio quality needs to be made clear in the listing. The missing Extended versions for the first two movies also needs to be clearly stated, and this 8-disc box set should not be labeled "Complete".
If you want to get the extended versions of the first two movies, that add $20 to the cost of this box set. It is exactly the same cost to get the individual Special Edition versions of every movie, plus you get a significant amount of special features.