The new 2014 Z28 has 1 speaker. It's for the seatbelt buzzer.I think most of the companies are getting wrapped up in speaker count instead of actual sound quality.
Mine isn't about volume, it's more about balance. The 10" sub does a pretty good job (its a shallow sub and doesn't go as low as I'd like) of filling the cab with the right amount of bass at moderate volume. I can crank it and rock out, but it's not obnoxious.
I'm only about half gain front and not quite 3/4 gain rear.