Can a center channel improve stereo music?

[krabapple]

Stereo is by definition, something that provide a tangible sense of a 3D image - it is unrelated to the number of channels. (The word's origin is the Greek word stereos (στερεός), meaning "firm," "solid," or "three-dimensional". )

The earliest use of the term in Audio was applied to systems that had 3 channels Left Center Right - that was the first STEREO sound.

Yup, going back to Bell Labs' foundational research on audio reproduction.