Any Shimano 9 speed specific STI shifters will work with your drivetrain. Do understand that there are a few differing brake compatibility combos for the Shimano intended braking action (although people intermix brake cable pull ratio levers and calipers with varying results). Knowing the caliper actual part numbers (which will then let you know which cable pull ratio they like) helps you/us be more specific WRT that aspect. I don't remember if the R550 calipers come in more then one cable pull, IIRC they are the "old" super SLR spec.


BTW one can hook up a shifter cable to a un mounted shifter and run through the gears quite easily, not having to mount the shifters on an actual handle bar. We do this at work sometimes to test systems before dealing with cutting cable casings and bar taping. Andy.