Let me try to answer your questions. The information below is based on the
owner's manual for the 6003 located on the Marantz website.
1. The HDMI outputs can carry audio as well as video. However, that receiver will not play audio from an HDMI source and output audio over the HDMI OUTPUT jacks at the same time. In other words, if you are listening to the audio coming from an HDMI source through the speakers connected to that receiver, then it won't output audio through the HDMI OUTPUT jacks.
2. It will not output a signal from both of the HDMI OUTPUT jacks at the same time. There is a button on the remote to allow you to quickly switch between the two outputs, but you can't have both at the same time.
3. Digital coax doesn't have the bandwidth to handle the new lossless codecs.
Adam