This has been addressed a few times before. The Sinar backs can be gotten with adapters. There is some possibility of the Hassy back (I think the CFV) if you find an adapter - Imacon made them, Hassy stocked them for a while, not sure what present situtation is. Many people have used these solutions with the flash synch cable.
The only factory kit worth noting (there were some early ones, but they were scan backs) was the dp20, using the P20 supplied to Rollei by Phase, and then put in a removable 6008 back. It integrates but in a simple way - no EXIF, no battery control, but no synch cable.
For a while you could supply Rollei with a Phase back of your choice and they would machine it into a back for $3k. I don't know if the present Rollei folks will still do that, or if Rollei Metric will. I don't believe they have any digital backs on hand.
In theory, it should be reasonably possible to substitute a newer Phase back into a dp20 setup, as the conversion path should be "legible" with the P20 as a mule (but still keeping the dp20 back), but I don't know anyone who has done it, and honestly don't really recommend it. If you try the dp20 (yes, I have mine for sale...) you'll find it is really pretty good.
Hope this helps. Also look at Pascal's Rolleiflex pages.
http://www.rolleiflexpages.com/
Geoff
