I hear that the "loop" machine only takes 15 seconds.
What about the loops I make in cubase and mixdown, do they have to fix themselves into those 15 seconds as well or can I Write my loops longer before I import them to the SP-555? I mean 12-hours of sampling time gotta be worth something.

The new SP-404sx can hold like a whole song (sample) on one pad. Is this possible on the SP-555?

Yes

Thanks for the quick reply!

also you may want to try resampling loops with slow changes in effects over like a minute or so

even though it wont loop at the end you trigger it and use the cues in the changes of effects to tell when its going to end.

allows for some fun chaotic moments and unexpected results