It started for me in high school in the 70s, where we obsessed about specs—THD, bandwidth. Late 80s was post specs—perceived accuracy compared to live, for me based a lot on written reviews of golden ears types. Now, its simply what sounds enjoyable. Smooth and capable of loud at no more than $1,500 per component. Imaging is not important to me, so I dont have to spend for that.
So, for me, ‘musical’ is what makes me feel good when I hear it. Most of that means not a lot of energy in the high frequencies such as crash cymbals and aggressive digital compression during mastering—and re-mastering.