Hi...Mint 9 Fluxbox is simply missing an audio configuration tool like "pulse audio volume control" which enables you to set your onboard souncard off when using an external one. But there should be a GUI which will enable you to choose a default soundcard and set it all up. This is what I really miss in Fluxbox compared to Gnome.
I had a problem using M-Audio delta 44. First of all it' almost two years since the default linux drivers stopped showing its analog outputs. This problem is solved on many forums by adding two lines to /usr/share/alsa/cards/ICE1712.conf. Why isn't this done by default, when this bug exists since Ubuntu 9.04.