I have a separate USB midi interface, I don't use the Quantum's interface. I am personally confused about the midi integration on the Quantum. So I assign the midi inputs and outputs for the instrument (you need to set up an instrument first for each midi controller or device you plan to use, in the main settings) to the ins and outs of the USB midi interface. Having said that, I believe my TD15 uses a USB midi connection so it is probably independent of my USB midi interface. I can't be sure without checking. I also have a Roland midi keyboard which connects in a similar way (along with an accompanying audio track), so it may well be that which is connected to my USB midi interface, and the TD15 has its own. So I created midi connections called TD15 Module and TD15 Pads, then assigned the outputs in S1 to module and the inputs to pads. Does this make sense?