Why? To replace all three units in each speaker will be far more than the speakers are worth. It would be cheaper to buy another set and if you are attached to the cabinets, swap the units. I would take the opportunity to upgrade. B&O passive speakers are cheap and some are true bargains!

The S55 is a nice speaker but the S80 and S120 are a fair bit better. And not a huge amount bigger. 

In addition to Peter's answer - you will not be able to source the original drivers as they are long discontinued and finding new drivers of the same spec's will be nigh on impossible. I'm surprised that you need to change all 3 though, the bass drivers I could understand as these suffer with foam rot but this can be repaired relatively easily. The mid range & tweeters should be fine unless they have been blown by being attached to a too powerful amp and played to death.

If you can elaborate on the problems then perhaps that would be a good starting point.

Chris.