In the world of digital audio, sound quality keeps increasing with each new format introduced. The increased audio decoding quality built into each player must keep up with the increased quality of the recording put onto each disc.
Connecting your old disc players to the latest high-end equipment over a DIGITAL audio connection is the best way to get the most sound out of your CDs and DVDs. In the setup below, if you spend a little more money on your receiver, then you can "skimp" on the quality of your disc players.
For most of us with older non-HDMI receivers (and some without OPTICAL or COAX), we're stuck with the ANALOG connections. In the setup below, you might be spending a bit more on your disc players (while holding on to your old receiver) to get highest sound quality currently available.
Here are some links below that might help answer any other questions you might have:
Completely UNCOMPRESSED Digital Audio
Dolby vs. DTS