Just to say that the Software verson of Dolby Headphone in PowerDVD isn't as good as hardware versions. I've tested it against a Xonar D2 with Dolby Headphone built in and the Xonar wiped the floor with PowerDVD. Comparing software DH to hardware SilentCinema wouldn't be fair.
Some DVDs have a pre-encoded Dolby Headphone soundtrack. Pearl Harbour has it. Shame about the film though. That might be a more suitable test.
I even got dolby headphone through my Essence ST now hasn´t tried it much. I get more distortion through the headphone output then the lineout on it.