Amplitube/iPad + Napster volume mixing?

[ronlitz]

I'm using Amplitube on my iPad with my iRig HD2 to play along with songs on the Napster app. What are my options for mixing the levels of my guitar and Napster? Specifically, I need to lower the level of Napster. The volume knob on the iRig just changes the level of the total mix of the guitar + Napster, and I can't increase the level of the guitar any more by increasing the master of the amp in Amplitube without adding unwanted distortion.