Just got a Shimano Dura Ace 7800 rear derailleur to replace my old fading Ultegra 6500. I plan to use the 7800 with what's left of my present Ultegra 9 spd system which still works great. Now the 7800 is advertised as being compatible with either 9 or 10 spd, but there are no instructions in the service manual on how to set it up for 9 spd. Any suggestions or instructions? Would appreciate any assistance. Thanks!