i don't use the loops so often, i've only used them on one track really..
If you use the "Arrangement" mode on the programmable rhythm, you can add different beats and fills to the entire track.
I generally set the tempo and use a repetitive beat, then i record my r. gtr and bass tracks and whatever else i fancy.....then i alter the drum fills and things at the end.
I do it all through the "Arrangement" menu.