Two different sound sources, two sets of speakers

Alright this may sound a bit confounding if I don't explain a bit so here goes. I got a new monitor for Christmas the Acer H213H, looks great 1080p and all, however there is a small problem when it comes to sound. The monitor itself has speakers, while I'm using the computer this is fine as I don't care how system sounds are and most of the time when I am playing a game I have headphones on.

However, I have my PS3 hooked to it via the HDMI slot. When the monitor uses the HDMI port it defaults to putting the sound through the speakers on the monitor, but generally these speakers don't get loud enough to really hear everything in the game. I tried simply plugging in a spare set of speakers I have into the monitor to see if it would output through them, but it won't. I have the option to play audio via the composite cables if I want and could plug them into RCA to mini-stereo converter and plug a set of speakers into my PC and simply put the audio from the PS3 into line in. I have 4 speaker ports, what would be best to plug it into? I have the option of front rear, side and center. Right now I have the monitor plugged into front. I'm guessing I'd want the other set of speakers in the front jack as well, but I though having them in a different jack may allow me to isolate the line-in audio.

Now to my question, is there any way I can make it so that The PS3 is the only thing that plays through this set of speakers without going and hitting mute on all other inputs? Does anyone know of an easier way to do this rather than what I mentioned above?

 

Nobody has any ideas on this?