Whatever it was recorded in.

My music listening is done mostly on my stereo, which is a much better system than my home theater anyway. I would like to get a DVD-A/SACD player for my stereo though, most of the listening I do with those discs is done on my home theater.

I've done the Pro Logic II music mode thing, it's interesting but far from ideal for a lot of music. It depends on what you're listening to, some of the definition and separation gets lost but for some music that doesn't seem to matter a whole lot. (calling it music might be a stretch since I find DPLII works best for modern/electronic technoish stuff). If you've got a good pair of stereo speakers the DPLII doesn't really add anything but if you listen to the right stuff and your speakers aren't that great, I can imagine it might be mistaken for a better more spatially "detailed" image.