The "early" AMX boarding thing really is nothing. It may be if you are with cruise lines with more passengers and big lines for embarkation but with RSSC it is really a joke. They do have a separate line for AMX at some embarkation ports but since there is seldom a line it really does not matter.

There are often vans meeting the planes and you just pile in and share the ride to the Intercontinental. No need to pre-reserve anything.