kevinhpp - thanks for the post. I posted similar issue on Live Sound Forum. I can't help you, but seeing your post tells me my problem is not unique and not a bad unit, just bad design. I ran Variax VDI to HD500X, then Link6 into L2T, then Link6 into L2M and had the same problem. Plug guitar/mic into the L2T mixer and get nothing in the L2M, but when I unplug the 500X, get sound from both speakers. Work arounds are fine (500X into the Line input or the XLR inputs) but kinda defeats the whole concept of the L6 system - like plugging a Variax into the POD/HD/Helix 1/4 guitar jack instead of the VDI, still works, but you lose the model switching that the VDI provides.