When listening to music on a plain CD, I have the choice of listening
using my Stereo PCM line or the 5.1 Analog line used for DVD-A.
(I understand that it would still be 2.1 Stereo in lieu of the 5.1).

Can anyone help me to understand which should give the most desired
result? Which option should deliver the most the CD has to offer?

I know it depends on the source material and quality of the recording as far
as which way sounds better, but I am curious to learn all I can on this one.