IMHO, I agree that the quickest and most comfortable way to return to the AKL would be the cab.
If you want to use the "free" Disney transportation, there are two options.
You can ask the Breathless Captain to drop you off at the boat dock near the entrance to EPCOT. Then you can walk back through EPCOT and catch the bus to the AKL from there. On our last Illuminations Cruise, the people we shared with did this. They did not have a problem getting back in to the park or to the buses. If you do this, take your time. Let some of the crowds diminish and enjoy the fountains and lights while you are strolling out. There's plenty of time to catch the bus. They run for at least an hour or two after the park closes.
You can also elect to catch a bus from the YC or BC to Downtown Disney and then transfer to the AKL bus there. This option could take more than an hour and I don't recommend it unless you want to get in some shopping or spend a few hours at the clubs on PI.
Enjoy the Cruise!