IMO, the term more musical refers to the overall presentation of a given work.
The pacing, smoothness, dynamics, harmonics etc. - everything one would hear with live music. Some amplifiers may sound very quiet with no distortion, but they lack the "soul" of live music...very analytical. Other amps sound very warm and overly smooth and veiled.
It is a rare amplifier or piece of audio gear that balances the extreme to find the nirvana which is "musical".