Best way to play backing tracks

[carvinae185@gmail.com]

In a two-person session today we noticed that the guy on the other end could hear my MP3 player running a backing track from my phone into my interface and then into jamkazam,  but when I started playing my guitar which is using a second jamkazam track it tended to drown out the backing song.... it seems like all of the various volume and pan controls that you see in the JK interface only affect what you are hearing with no ability to adjust the balance between multiple sound sources as heard by your friends....... and on their end they seem to only have a master volume in terms of what you're sending them.....
this could very well be an interface problem since I'm using a Roland HS 5 session mixer that I don't fully understand yet as my interface....
the Roland has four stereo channels and those all show up in jamkazam via the asio driver.