To simplify matters I would consider removing one or two, unless you need
three for some reason. Go to Settings Manager, Sound, Device. Click on the down
arrow and choose the one that you want to use. They should have distinct names
and be numbered in order from zero. Uncheck the boxes of the ones that you do
not want to use. Make sure that your speakers are attached to the right card.

Ok. Got that. But there's a but...

the front output is considered a second soundcard. But it's onboard. The
back outputs are considered the first. And a soundblaster is considered the
third.

I do need to use both front and back outputs.

Then, I still get the problem.