The difference is in the quality of components put inside, the amount of research and development put into it, reliability so that the device lasts for a number of years. All these factors and more decide the price. The dac also makes a difference. I think you are using one dac from all your different sources, so chances of observing a difference is very less.
I do understand what you are trying to say, most of us have gone through that and still going through it. Hence the suggestion, if it does not sound weirdly bad to you and you enjoy the music, don't add doubts to your mind, sit back and enjoy the music.
In the mean time, visit audio outlets and audition various speakers, amplifier, receiver, etc. That will give you a benchmark or a baseline you can aim for to achieve in your home. You can carry your own music to those outlets.
MaSh
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