I know, you've expressed this preference for the full 6/7 bath process before, but do you actually have any evidence that it gives "better" quality, or has other merits such as solution longevity?
I can't tell the difference between Tetenal/Adox (about 110 films) and Bellini (40 films), but that's just a subjective impression and not based on any careful comparison. I can certainly believe that the 6/7 bath process is "better" but would love to see the evidence.
Main issue is the combined bleach-fix, and reusing it in the kits. The times get very long, and there have been issues with longevity of the slides, as some of these kits omit the stabilizing. Weak bleach can lead to retaining of silver. In most cases, this does not affect very much the look you will get. but I have slides processed with press kits from 1980's, that do have already problems with fading colors.
Making corrections if needed is also harder, because almost all reference available is for the official process. As you may know, I also have been promoting the use of chemistry with separate bleach and fixer for C-41.
The Tetenal (ADOX) is the original formula for a 3 bath press kit, and it is the best of those. This can't be said about every other kit there is available.
For longevity - no. E6 chemistry does not keep very well (compared to C-41 for instance). There is no difference I have noticed between the press kits and 6 bath E6 in this sense, that I have noticed.
In scientific sense, I can't provide you with hard evidence on this. I don't have densitometers, or have the means of standardizing the process up to a point this would be possible.
