I used to have that button, and used my Mac to play my backingtraks. Yesterday when I should test, I didn´t get the possibility to take it out on two outputs. I usually put click track on AUX and the rest on USB. Maybe I have to just pan L/R when I use the Mac. Gig tomorrow, so I have to get every thing to work properly. I have an iOS, so can use that for the gig.