I have a pre 2011 Sony DVD player that has Composite, Component and Digital Coaxial out ports. It was manufactured and bought before the AACS Adopter Agreement of 2010 that made manufacturers downconvert component output to 480p.
How do I ensure I am getting HD instead of 480? I know that the picture I get with component is superior than the one I get with composite? Also can I use Digital Out Coax for Video or is it only for audio? If I can use Digital Coax for video, is it better than component?
Many TVs have an info button that will tell you what the resolution of the content is.
Your problem is that DVD players don't output in HD regardless of the output connector.
Best you can get is 720 x 480 in NTSC and 720 x 576 in PAL. Both are substantially less than 1280 x 720p. Component video looks better for other reasons.
The digital audio output is just that audio not video. TVs don't have digital audio inputs. It was meant to connect to an audio system so you could get Dolby Digital and DTS surround sound.