So I got a pair of Tritton AX Pro True 5.1 Dolby Surround Sound headphones, and am absolutely loving them. However, I am wondering why I cannot get dolby to work, and instead get PL.

With my headset hooked up to my optical out on my computer and plugged into the decoder box. I get the power on LED ( http://www.destructoid.com/destructoid-review-tritton-s-ax-pro-headset-125869.phtml )
Which is the top most LED.

After going to Control Panel-->Sound-->Playback-->HTO Striker 7.1 Digital Output-->Properties-->Supported Formats then running a test on the Dolby Digital format, it will cause the second LED to light up (which is supposed to be Dolby true 5.1). The test goes through all the speakers in the headphones and they all work.

Since I am on my PC, once I go into play a game (Bioshock 2, Bad Company 2, etc) it switches the Dolby Digital LED to the third LED which is PL (not sure what this stands for).

Any one know why it's switching over and how to keep it sitting on Dolby Digital?
And what does PL stand for exactly? Google searching bring up nothing.