Pro-Logic II builds on the original Dolby Pro Logic (which in effect is Dolby Stereo in the home) with improved channel separation and a dedicated LFE track.
http://en.wikipedia.org/wiki/Dolby_Pro_Logic
Since the source is still a Dolby Stereo mix though, the results aren't as profound as something with DPII in mind. However, it does tend to sound better anyhow. I've been using Pro Logic II to decode LaserDisc PCM tracks for awhile now and it does do much better channel separation as well as overall dynamic range in all channels. Temple of Doom on Laserdisc is an undeniably delicious treat!