Perhaps everyone discovered torrents for Kontakt and Turnado, but since I have the thing and mostly just used it for a drum module for a few years, I've started messing with the SP more...
I've been playing with making beats/etc in Reason 4 and sampling from that over USB to loop capture. Works fine for me. I tried to do so with FLstudio 8, but my latency seems better with Reason. I don't have to record silence and etc first to get perfect loops. If I get a bad loop with loop capture, it's computer latency, or I had human latency pressing record or footswitch, or I tried to sample something that's sustaining and chopped off the ass end. Chopping off something not at a zero crossing on the waveform tends to be glitched.
I've had mixed success with trying to trigger MIDI while recording a pattern in the SP-555. I think it's my latency in Cubase, but every once and a while I hit "GO" on both at just the right time.