Sirius XM falls short of revenue estimates in its latest quarter.The bar of expectations was low heading into Sirius XM Holdings' (SIRI -5.02%) second-quarter results on Thursday morning. The satellite-radio provider still bumped its head against the limbo stick. Revenue clocked in at $2.18 billion for the three months ending in June, a 3% decline from where it landed a year earlier. Analysts were holding out for just a 2% dip.The year-over-year decrease in business may not seem like much, but it's the seco ...