vocal tracks with onboard backings

[Senn5]

Has anyone tried this on the sx900?
I have seen a couple of videos but can't quite get my head around this.
I have a vocal track of a friend of mine on a song we did years ago in Sonar. I can save his voice track as a separate wave file, but sure how I get that into the sx900 to play around with some styles and redo the song.
Any thoughts are much appreciated.
Thanks in advance.....