"John Leventhal did the bulk of his mixing on a pair of small Radio Shack speakers. (Leventhal, a famous New York City-based guitarist, songwriter, and engineer, made his mark by producing Shawn Colvin's acclaimed 1989 record, Steady On.) Leventhal owns both a pair of Yamaha NS-10Ms and a pair of Radio Shack Optimus 7s. But he prefers the latter."

Mixing depends a great deal on the person doing the mixing. The speakers are only one part of the equation and as you can see from the above example, not necessarily the most important part either.

Best,
Mike