SiriusXM shares are up about 2.3% in pre-market trading today after the satellite radio broadcaster announced that it ended Q2 with more than 25M subscribers, a net addition of 715,000 — well ahead of analyst expectations. The increase in the quarter is 15% higher than the increase in the same period last year, a new record for the company since Sirius and XM merged in 2008. As a result, execs now expect to end this year adding 1.5M, up from their previous prediction for +1.4M. CEO Jim Meyer calls the Q2 results “an exciting new milestone” that should “bolster SiriusXM’s leadership position in a dynamic audio entertainment marketplace.” The company reiterated its forecast to add 1.6M self-pay net subscribers in 2013. Most of SiriusXM’s new customers are auto buyers, and the company attributes much of its recent growth to the continued strength in that market. Sales in June were up 11.2% vs the month last year, to a seasonally adjusted annual rate of 15.98M, Automotive News reported.