I'm not sure if it's fun and it certainly isn't easy, but Open Modplug Tracker offers minute control over samples/instruments and supports a lot of filetypes and plugins.

In addition, if your game can play mod music, you won't have to use compressed waves and may be able to manipulate playback from code.

It's free music creation/editing software: http://openmpt.org/features


Inkscape is an open source vector graphics editor: https://inkscape.org/en/