I'm sure I'm far from the only one in this boat, but I haven't been able to find many posts on the subject. My primary focus is 2 channel audio, but I use my 2 channel setup to playback audio when I'm watching a movie. My 2 channel system is only stereo: a Rega DAC connected to an integrated amplifier.
Most blu-ray players can of course downmix all the surround formats to 2 channel stereo, but I've been getting into the HTPC scene, so I'm using my computer to play back blu-ray movies rather than a blu-ray player. The HTPC scene's preferred method of playback software doesn't offer very robust downmixing support, and offers essentially no DRC support for those late-night movie watching sessions. So it seems like a home theater receiver or processor would probably be a better tool for downmixing to stereo from a bitstream of the original multichannel soundtrack.
For those of you using a 2 channel system for movies, how do you mix the surround audio down to stereo? Your blu-ray player? A surround receiver or processor that comes before your 2 channel amplifier?
Many of the different Dolby and DTS surround formats (if not all) can carry metadata that instructs the decoder how to downmix to stereo, if the audio engineer provides that data. If the audio engineer provides that data, I'd imagine that the downmix wouldn't vary much, if at all, across different receivers and processors. But, if that metadata isn't provided, I'd imagine that different receivers and processors may use different algorithms to create a downmix.
In a perfect world I'd like the receiver or processor to have an optical or coax SPDIF output so that I could send the downmixed 2 channel PCM signal to my DAC, but I haven't been able to find a single receiver or processor that cites the ability to downmix a surround signal from the HDMI input and output that signal over SPDIF (which seems odd to me, since many blu-ray players can output a downmixed stereo signal through SPDIF).
Anyway, I'd be interested to hear about any of your playback methods!