5.1 systems do not ruin the sound from music. As you said yourself, it's recorded in stereo. As such, the output is stereo. TWO FUCKING SPEAKERS. I tested this yesterday. I listened to each speaker. Only the "front left and front right" aka: "regular stereo speakers" were putting out sound.
Now just in case I was being screwed here. I fired up quake 4, turned on god mode and stood in the middle of a room full of enemies and spun in circles. The sound moved. Therefore, the 5.1 works.
In conclusion: 5.1 DOES NOT fuck up your sound, it merely plays it as regular stereo sound, the extra 3 speakers merely wank-it and wait for you to put in something done in 5.1 sound.
Now just in case I was being screwed here. I fired up quake 4, turned on god mode and stood in the middle of a room full of enemies and spun in circles. The sound moved. Therefore, the 5.1 works.
In conclusion: 5.1 DOES NOT fuck up your sound, it merely plays it as regular stereo sound, the extra 3 speakers merely wank-it and wait for you to put in something done in 5.1 sound.