Besides the Capreo lockring and lockring tool, only the actual Capreo hub and the smallest 3 cogs on the Capreo cassette must be used in a Capreo system. Everything else is interchangeable with other Shimano components including the derailleur, shifter, and 6 largest cogs. I've used a Dura-Ace derailleur with Capreo hub and it shifted better than the stock Capreo derailleur (although I used an XTR shifter with the DA).