Boss BR800 frustration

[Pragmatist]

Managed to put some backing tracks in WAV format onto the SD card and they play perfectly well in song sketch however there is no option to to be able to play my bass over the top. 
what am I doing wrong?

 

[Earbrass]

As nobody here seems to know the answer, could I suggest you try asking on the Roland Clan forums?

https://forums.rolandclan.com/viewforum.php?f=24