I see you already have the answer directly from the source. Thank you Johannes for your participation in the forums. Much appreciated!
Wilbur, you didn't mention if you are using film or digital backs. I have both cameras 6008AF and also a Hy6 and an AFi body. Mostly I shoot with the digital backs but also with film. I have noticed that the metering works very well with film on the 6008AF but not always consistent with a digital back fitted particularly with the flash attached (metz 3652). I have wondered if reflections off of the digital sensor could be causing the metering to be off on occasion. Maybe depends on the lenses used and direction of the light sources too? Johannes do you know anything more on this? Anyhow, the metering with digital back seems to be improved with the Hy6 - much more consistent. I have been truly thrilled with the metering for film on the Hy6. It's quite an amazing camera.
I'm sorry that in the moment I can't provide complete information, because this is an issue which concerns an former engineer who is allready in his retirement. The best I can tell you for now, is what you might allready guess: the 6008-system was developed and optimized for the use with film backs, its concept goes back to the beloved SLX66 from a time when nobody knew how to even write digital back
Of cause the 6008 was a much improved system but it was still an expert in the analog world. When the digital backs came up and became more and more affordable, the DB-producers such as P1 and HB developed also interfaces for 6008-system. But i was allways meant as a compromise.
The Hy6 on the other hand was allways meant and developed as an hybrid to serve the wishes of customers of both world, analog and digital.
Like I admited above, this a really easy and superficial but i think it explaines why there is a difference between 6008 + DB and Hy6 + DB
I'll try to dig a bit deeper in the next days an give you some better information.