I did a little bit of reading on the subject and it appears that Dolby Pro Logic can take a matrix encoded stereo signal and decode a four channel surround sound field with left, center, right and a mono rear channel. I THINK it requires a stereo signal that's been encoded to do this to the sound.
Pro Logic 2 can take an ordinary stereo signal and decode it into a 5.1 surround sound field and it requires NO matrix encoding to make it work. It will produce left, center, right, stereo rear channels AND a sub woofer output.
With this said it appears that Pro Logic 2 would be the way to go for the time being with the Roku box. I'm going to experiment with it some more this evening.