Yamaha DTXpress/DTXplorer/DTXtreme

Hi guys,

I just got my DTXII and I'm wondering if there's a way to layer a 
walking bass line over a bass drum sound. I don't want to trigger a 
loop, but have the bass line advance one note every time I hit the 
kick. The manual explains how to do it with a pad song, but I can't 
seem to be able to layer the pad song with a kick sample.

Any help would be greatly appreciated.

Thanks!