It's included in the spec for DVD-Video - 16-bit, 48kHz 7.1 channel PCM audio. So, are there even any authoring tools to do this? And then, are there any players capable of it? It's so obscure, but it'd be an interesting experiment to just try out. I wonder if any players could do it over HDMI rather than analog out.
Can't be done. Despite it being included in the DVD-Video specifications, it was never enabled in any player yet made. (It was always an optional form for DVD-Video, and was dropped because it left no room for any video input at anything remotely watchable quality-wise) DVD-Audio was developed to do this instead - and DVD-A does not use 7.1 as there is as close to no demand for it at all as makes no difference. Reasons? Too many possible setup options.
