Gerald, there is more to stability than the stabilzer in E6. It also involves silver removal and the pre-bleach chemistry as well as sulfite content in the process and pH which relates to retained developing agent.
The dyes in all commercial films today are so-called 'kodacolor' dyes dispersed in some medium in gelatin. Agfa uses a method much like Kodak, now that the bulk of the Kodak dispersion patents have expired. The generic dye structures are cyan - phenolic, magenta - pyrazolone and yellow - acetoacetate in all films regardless of manufacturer. The specifics relate to how they are incorporated, what is in the film to enhance dye stability, and what dye hue was chosen among other factors.
Yes, Agfa and Fuji can go through Kodak chemistry and vice versa, but I have no idea what this does to the dye stability each of these companies expects by design of their products. I have seen some pretty bad disasters, even when things go right. After all, my properly processed Ektachromes from 20 years ago look pretty bad, but some are just fine.
I just made a post about mixing C41 chemistry. I'll reiterate part of it here adapted for E6. The developer pH values in E6 should be within about +/- 0.1 units at 20 deg C with a calibrated pH meter. Some ingredients must be controlled to within +/- 0.1 g/l or even +/- 1 mg/l to control color reproduction.
I think hand mixing is elegant, but not worth the trouble when the potential for losing good pictures is the alternatiive, even if it is just a hobby. I spent a whole day photographing waterfalls and cliffs at a park with a friend this weekend. I would hate to see any of that hard work lost, hobby or not.