I've been hearing only the front speakers for some time. The back speakers work, to be sure, but I figured that ordinary mp3's were incapable of surround sound as they weren't created for surround. So, I was content to have only the front three speakers playing unless I was in a game like Knights of the Old Republic. However, on one of those rare moments I got out of my computer chair (I had to clean my room), I had music going on, a mp3 from edgen.com. I bent down next to my rear speaker, and lo and behold... sound!
I reset the balance to favor the back and side. All speakers were set to 100%, but I took the front left, right, and center down to 50%. Then I turned it up. Now, I have sound out of all my speakers. I am of the mindset that good music is meant not to be heard, but experienced, so this is good news for me -- very good news. However, I have to ask: What makes a sound "surround sound", then, if all my sounds can be heard out of all 8 speakers?