PS3 usually avoids bitstreaming anything from HDD... it will ignore your BD/DVD settings. But there are some workarounds.
First DTS is handled by the "Keep DTS in audio stream" feature of PS3 Media Player, this will fake out the PS3 to pass it through to your reciever.
As for Dolby Digital/AC3 5.1, the PS3 will try to decode it to PCM if you allow it to output 5.1 PCM. Go into your audio settings and adjust the output, select HDMI, manual configuration. Check Dolby Digital 5.1, and uncheck all 5.1/7.1 PCM modes. Also go into PS3MediaServ, general encoding options, and tick "remux when audio is AC3". This will allow DD 5.1 passthrough straight from your file to the reciever. For some reason Sony prefers to decode to PCM if given the chance, but they mess up something very badly with the subwoofer channel at least, the difference is very audible. Note that while this setting is in effect, you're also going to lose PCM surround for your games, but many of them have Dolby Digital Live 5.1 support.
For Dolby Digital Ex, HD audio formats, I have no clue. :p Generally PS3Media is going to convert to AC3 if it can decode it. If the DTS streaming trick were easily ported to other formats, it would be nice to have.