SP-FORUMS

use the affect assign button instead of the remain button, it does exactly what you you're trying to do

use the SP-555's effect assign button to assign (and remove) affects to specific pads. you can even use the affect to assign affects to pads on different banks aside from the main bank you're using (only while in sequencer mode)

I have a video of myself doing it in real time if it helps:
http://www.youtube.com/watch?v=NqisETyTobY&noredirect=1