BleepingComputer.com: I'm confused about how to properly set up computer speakers with my Xbox 360 and LCD monitor.

I'm confused about how to properly set up computer speakers with my Xbox 360 and LCD monitor.

I have the console hooked up to the LCD monitor via a HDMI cable, and I was getting volume as normal that way, through the monitor's own speakers, but, even at the max volume, some games are too low, so I decided to attempt to go the route of using computer speakers connected to the LCD monitor to hopefully act as the audio instead of the monitor's speakers.

I just received computer speakers I purchased online and plugged everything in where they belong, but the volume is simply coming out of the monitor's speakers like before. I'm totally new to this sort of setup, so is there some detail I'm missing somewhere? Or perhaps this sort of setup isn't even possible? (I assume it's possible because the monitor itself has a green audio jack/hole in the back, as if for optional speakers.)

The LCD monitor is an ASUS VH236, and the speakers are Packard Bell Platinum JBL Series.