inherent balance is one thing.

exhaust sound is another thing. The exhaust sound is largely determined by the spacing of the exhaust pulses.

An inline6 has regularly-spaced exhaust pulses, which makes it sound the way it does. A Porsche 911, with its flat-6 (perfectly balanced also), sounds distinctly different from an inline6.

A (typical) V8 will have pairs of exhaust pulses bunched together, which will result in a "burbling" exhaust sound.

When we say an engine is "smooth", we are also referring to the engine sound quality, aside from the lack of vibration.

For me, the appeal of an inline6 comes from the thought that there are no unnecessary internal stresses on the engine internals due to imbalance, and the engine feels and sounds perfectly happy at any RPM. Plus if it's a Benz engine, it can run at redline all day long ...

And since my car has a 5spd manual, I use engine sound as an "aural tachometer". Or I just listen to it because it's music to my ears ...