Pro logic II turns 2 discreet channels into 5.1 channels.
Pro logic IIx turns 2.0 and 5.1 discreet channels into 7.1 channels.
and then we have Pro Logic IIz
To Mad Lust Envy :
If we set the input to 7.1, and turn DH on, we always get virtual 7.1, no matter what game we play ? [Games could output 7.1 or 5.1 channels]
No. The game must have discrete channels built into its sound. For example, lots of indie games only do stereo.
But for most standard titles, yes, you'll get surround.
If listening to music, just uncheck the DH button in the U3 software settings.