A question I raised before involves video in that can one hdmi input (from a Tivo or blu ray player) go to two hdmi outputs (TV/Overhead projector)...
The 976 can certainly output the signal at both HDMI outs at the same time. But, if you have a 4k signal it would be reduced to 1080p at both outputs. That's the only limitation I'm aware of.
Don't know about the Marantz.