Contrary to your first stated assumption, there are a great many of us who use a tuner, a record playing system, a tape deck, and a CD playing system that does not have balanced connections or a volume control, as well as other sources. For those of us misguided souls, a preamp is kinda handy for providing gain, volume control, RIAA equalization and source selection and to balance the stereo signal between channels, in case our hearing is better in one ear than the other or a room problem causes the imaging of our speakers to be off-center. So preamps are not merely empty boxes, do serve a function, and are not a perceived need created by marketing programs designed to deceive. If your only source is a CD player with balanced outputs and integral volume controls, and you are happy with the sound from it, then you don't need a preamp, and no one is putting a gun to your head to use one.
By the way, why don't you try out with and without a preamp in your own system and listen for yourself instead of relying on what others have said? If you tell me you can't because your CD player has no volume control, then I'd say you could definitely use a line stage, either active or passive, unless you are willing to put passive attenuators on your amp and adjust them with each disk (and possibly track) you play.
By the way, why don't you try out with and without a preamp in your own system and listen for yourself instead of relying on what others have said? If you tell me you can't because your CD player has no volume control, then I'd say you could definitely use a line stage, either active or passive, unless you are willing to put passive attenuators on your amp and adjust them with each disk (and possibly track) you play.