Surprise, surprise you made it with a DR-880 ... which I have owned for years! I guess the phonebook-size manual turned me off so I never even toyed with the composition capabilities. I only used it, very rarely, for it's drum/jam tracks. Like almost everything I've ever bought with a "bajillion presets" - i find practical use for about 5.
So you've inspired me to dust off that big ol' fat instruction book and see if I can't get a handle on creating some backing tracks. I had asked about your bass line because I had often thought that the 880 would be much more useful if I could change the bass lines. Turns out I can ! I'm an idiot. A lazy idiot. So lazy I'm going to check youtube for tutorials before I even dive into the 880 scrolls. :)
T-Care, Ken