There should be a "setup" or "config" file in the game directory. Delete it and run the game -> the setup will start automatically.
You could also start the game with a command line parameter telling it to use a different config file then default, but I don't remember what it was.
The setup for soundcard only is present only in the CD version to my knowledge. The floppy version has a number of settings to be messed with.
Other than that - try downloading and running this version of the game:
http://www.abandonia.com/games/en/49...lIllusions.htm. See if it works without the problem.
Oh, right. I've remembered something new: try fiddling with the FULLFIXED setting in your DosBox config file. Might help.