What does modern stereo sound mean? What's the difference between traditional sound and traditional sound?

Only traditional music and modern music.

For example, symphony is traditional music and DJ rock is modern music.

There is no such difference in acoustics. A set of the latest stereo can play both modern music and traditional music. HiFi audio can play the sound of sound source with original flavor and high fidelity.

Some sound quality sellers talk nonsense that his speakers are European and North American sounds, which is the result of being fooled by his own ignorance of music.