Complex sentence: The order of countdown was originally decided by a mix of record sales, radio airplay, video spins, message board posts, and conventional mail, but since 2006, supposedly online votes have directly influenced the countdown.
Split into simpler sentences: The order of countdown was originally decided by a mix of record sales, radio airplay, video spins, message board posts, and conventional mail. A combination of record sales, radio airplay, video spins, message board posts, and conventional mail would decide the order of the countdown.