If you haven't done so, go into the EAX Console > Speaker Settings and do a Speaker Test.
If the output to the speakers are correct, then it's not your soundcard or speakers.
Go into Winamp, Preferences, then click Output under Plug-ins, double click DirectSound Output in the Output plug-ins box and make sure Allow hardware acceleration is checked. Also, try changing the device from Primary Sound Driver to SB Audigy Audio 2...then check to ensure that the Device info box shows Speaker setup: 5.1
|Desktop PC| |Macbook Air 13" (Mid 2013)|
|Windows 8.1 Pro (x64)| |AMD FX 4100 Black Edition 3.6 GHz @ 4.0 GHz OC| |Arctic Cooling Freezer 13 PRO| |Gigabyte Nvidia GeForce GTX 560 Super Overclock 1GB| |ASUS M5A78L-M/USB3 Motherboard| |Samsung 840 Pro 256GB SSD SATA III HDD| |Kingston HyperX 8GB PC3-14900 DDR3-1866| |OCZ ModXStream Pro 700W Modular PSU| |NZXT Vulcan Micro ATX Case|