XM Satellite Radio, the larger of America's two satellite radio rivals, last week reported slower subscriber growth in the year's second quarter, attributing this to problems with product availability and slackened retail sales.

Sirius Satellite Radio, meantime, added far more subscribers than its rival during the same period, bettering analysts' expectations and continuing to benefit from signing schlock shock jock Howard Stern, who debuted on Sirius at the start of this year.

XM added 398,000 net subscribers in Q2, well below Q1's 568,900, lifting the total number of subscribers to 6.89 million. Analysts had been expecting about 430,000 net additions. Sirius said it added 600,460 subscribers, ending the quarter with 4.7 million overall.