John, How do you usually monitor what you're playing? Describe the route you take to get music in and out of your computer.
In your sequencer make sure that each audio track says something like
IN: Yamaha MW 12
OUT: Yamaha MW12
I had a look at that mixer on Yamaha's site. It's made for home recording that thing. You can surely do all your ins and outs simultaneously and monitor it all in wondrous stereophony on cans via the headphone jack on the mixer.
I can understand though you're having a hard time with an English language manual though mate...
