I'm an audio purist [read 'snob']
So, for me, it's always 2-channel stereo, and analog playback when possible. I have never experimented with more than a 2 speaker array for playback [other than subwoofer systems], so I can't have an opinion. I do know that the music you listen to on CD was almost surely recorded in stereo. Encoding to 5.1 can't *reproduce* information that wasn't there in the first place, so it can only
synthesize it, using some fancy post-production algorithm that doesn't exist
in situ. If I understand correctly, that is what happens; there is a lot of *digital processing* going on, to simulate a *surround-sound* environment out of a normal stereo recording.
There's a reason that Quadraphonic recordings and their brethren never became popular. [I'm sure you remember those]
That being said, the die-hard gamers here SHOULD be able to weigh in, because the 5.1 setups are VERY popular in the gaming arena. In games, especially shooters, there is an expectation of sound effects all around you - left, right, front, and back. 5.1 enhances the experience. But with music? It's not really natural. The sound source is in front, and stationary. Of course, there is sound that bounces around off walls and etc, but that is also picked up by the same microphone array when recording.
The very, very best recordings of classical music were made in the 1950s and 1960s with a 3-microphone array where the three mikes were within 2 feet of each other. This most closely simulated the human hearing process These were the famous 'shaded dog' RCA recordings, which are rare and valuable now. The most important thing is that the microphone technique has withstood the test of time.
In the end, it's what sounds good to you. Try encoding the same CD both ways, and see what *you* like better. It doesn't matter what *I* like.