Low volume on four speaker setup?

[BlueWeasel]

I have a Monster Sound MX300 with a Polk 4 speaker setup with subwoofer. The problem is I have to raise the volume control in Windows to the highest setting and there is still not enough sound coming out of the speakers even with the volume turned to the max on the speakers.

If I plug in my old 2-speaker setup, then the volume control is fine. Does my sound card just not have enough power to get enough juice to 4 speakers? The specifications for the 4 speaker and my old 2 speaker setup are pratically identical, so I know the speakers are strong enough.

Is there any way to make these speakers louder? It is just funny that I have to turn the volume on the speakers to over half volume just to be able to hear something.