I have both and I prefer the C55ES. But you should know that some early 555ES' (like mine) have issues with the transport that causes them to occassionally make a mechanical thumping noise when playing SACD's. Sony service (Bristol, PA) was unable to fix this problem for me, either.
So if you get a 555ES try to get one with a later build date (mine was built in 2001).
Mark
So if you get a 555ES try to get one with a later build date (mine was built in 2001).
Mark