those are simply pre-processed analog signals split from 1 cable into 6 cables. it's still the same quality of that cable. odds are, your receiver has FAR better circitry for decoding (DAC's) than your dvd/blueray player does.B you forgot about the direct 5.1 outputs that some devices have. I would have to say that they rate between composite and digital coax
ray/dvd -> optical/hdmi -> receiver = best sound.
hdmi supports hdcp content. most players limit component to 1080i, for ripping reasons, even though it supports it because it is not hdcp compliant.component cable can provide up to 1080p, as does HDMI. Why HDMI then?
plus, it also carries digital sound on 1 cable instead of 4+ (component + audio cable(s)) for ease of hook up