Back in the day I built a small switcher using a couple flip-toggle switches so I could switch between CD output and Amiga output.
But then you can only hear one or the other. I think gizmo350 wants both, so that you can hear CD audio in games and sound effects from the Amiga.
Best bet would be to find a simple stereo audio mixer somewhere. If you're handy, you can google the schematics for some simple mixers and build one yourself.
