Hi Walter,
I was looking at the specs on the 0404, it's not really a soundcard its a USB 2.0 Audio/MIDI External Interface, and it's not a 4 track mixer, the specs show that it has just 1 stereo output via several stereo outs that are all the same signal, so unfortunately seems to be limited to just 1 stereo output. No matter what you do with the mic and other instruments before going into the 0404, you will always end up with 1 single stereo out coming out of the 0404. Why not record straight into the 8 track mini-disc recorder, if it has 8 outputs then adjust each individual level, then send the mix to the 0404.
Gary