Try going to Sounds and Audio Devices in the Control Panel. Under the Volume tab, in the Speaker Settings section, click on Advanced. Change the speaker setup to your matching setup thru the drop box.
Also, if you have the speaker icon enabled in the system tray, see if your rear speakers volume is turned up. Double click the system tray speaker icon, click options > properties. Then, you'll have to find if you have the "Front/Rear Control", because I'm not sure if it's the same as mine. I have an Aureal Vortex 2, baby...
I hope this works out for ya. Good luck!
Bryan
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