What format can powerdvd6 successfully play in 5.1 and be able to use the "dolby headphone" feature? I tried 5.1 wav and wma, but they get automatically downmixed to stereo when playing.

I'm a little confused by that question... Dolby Headphone is mixed-down to 2-channels.

I don't use PowerDVD, but perhaps this will help:

There are several versions of PowerDVD. The free version that comes with DVD drives may not support Dolby 5.1 surround. Here's the comparison chart for the current (version 8) non-free versions.

5.1 WAV and WMA are not "DVD compliant". You won't find those formats on a commercial DVD, and PowerDVD apparently does not support these.

Your soundcard/soundchip may configured for downmixing. You should have a manufacturer-supplied utility to set-up its features.

I know that the dolby headphones are downmixed, but now when I try to play 5.1 files, it downmixes them automatically, not according to the Dolby headphone specifications. Even on 5.1 speakers it's still stereo. In WMP and Creative it's still 6 channels, but power dvd downmixes them improperly. They should let dolby headphone technology downmix it properly for headphone use, not downmix them automatically and killing the dolby headphone option.

I have the powerdvd6 deluxe, it does have dolby headphone.