I rarely go on chat but I seem to remember that it is an applet.
If it is an applet, the applet needs to be coded to use the Java Speech API. You would need to make some changes on your end, too, like using the Java Plug-In rather than the browser's JVM and customizing the security settings. Do you get a SecurityException when you try to run in the Main room?
If the p2p works, it sounds like the applet is coded to allow accessibility or to use the Speech API. There is a AccessibilityBridge that is supposed to map directly from Java to native methods, too, but the docs on that seem old. It's all speculation unless I dig deeper, and I don't have a text to speech engine myself. I don't think I even have the sound card in my main machine.
Working intermittently (p2p and not Main) is a bitch to debug. Harder still without source.
Here are a couple URLs for more info on speech engines with applets.