I just got this unit myself. I also beat my head against the wall trying to figure it out. From what I can tell (and still odd to me), if I hook it to the computer, I can hear all input channels through the headphones/monitor. If I use it standalone in mic preamp mode (not connected to a computer), I can only hear inputs 1 and 2. You have better luck since your post here? Are you getting the same results? I wrote Tascam a couple days ago but it appears their support is as bad as I have read about.