I wish I could tell you what's wrong, but I do not own the Titan Attacks game, so I have no clue as to what is happening. Perhaps you should also post this question on the Steam forums.
You say this is a Java game. You could try installing my minecraft
package, which is also a Java game, which needs OpenAL for sound. If sound is broken there as well, you know that it is not Steam or the Titan Attacks game.
Contact me in private (my "@slackware.com" email address or by posting to http://alien.slackbook.org/blog/your-feedback/
) if you have issues with getting Minecraft going because I think that is off-topic for this thread.