The military emblem of the Old Republic was an 8-spoke wheel. The Empire's is identical, except in that it has only 6 spokes.
What I found interesting was that the emblem of the Seperatists is a blue-and-white hexagon...6 spokes. Perhaps this is more symbolism?? Palpatine was pulling the strings on both sides of the war, why not combine both once he acheived his goal.