4.1 Surround Sound does not work(Rear Speakers).

[lidex]

Can you be a little more specific?

Intel 915G 	 
915M03-G-8EKRS2
915G7MC-8EKRS
915G7MC-8KS
915G7MC-ES
915G7MH-S
915G7MC-S
Intel 915GV  
915GV7MC-S
915GV7MH-S
Intel 915GL 	  
915GL7MC-ES
915GL7MC-S
915GL7MH-S
Intel 915P 	  
915P7MH-S
915A01-P-8EKRS2
915A01-P-8KS2
915P7AC-8EKRS
915P7AC-8KS
915P7AD-8EKRS
915P7AD-8KS
915P7MC-S
Intel 915PL 	  
915PL7AE-8EKRS
915PL7AE-8S
915PL7AE-S
915PL7MH-S

[satyanash]

I just wrote down the model number from the motherboard's windows driver installation CD. But I guess that's a generic one, meant for a series.
Parts of the sudo lshw command that you might find helpful:

*-core
       description: Motherboard
       product: G31MXP/G31MXP-K
       vendor: Foxconn
       physical id: 0
       version: FAB:1.0
       serial: UY31006009885

*-multimedia
             description: Audio device
             product: N10/ICH 7 Family High Definition Audio Controller
             vendor: Intel Corporation
             physical id: 1b
             bus info: pci@0000:00:1b.0
             version: 01
             width: 64 bits
             clock: 33MHz
             capabilities: pm msi pciexpress bus_master cap_list
             configuration: driver=HDA Intel latency=0
             resources: irq:16 memory:fdff8000-fdffbfff

Meanwhile I will open the cabinet/case/box and try to find out the actual model of the motherboard.

Satyajeet