As well as Drag & Drop, you can Audio > Export each wave track you require separately to a another folder before using Audio > Import each track to an highlighted blank track in your other file. There has always been a problem with dragging a wave track into RealBand in so far as the program seeks to load each new wave to track number one successively thereby overwriting any wave track already there. A workaround is to use Track > Insert Blank Track at track position 1 before dragging in the second wave file.