So, finally, satellite radio operators XM and Sirius announce today they’re going to merge. Which means Howard Stern and Martha Stewart will pair up with Oprah Winfrey and Ryan Seacrest. (Like they’re not already over-exposed.) But whether antitrust and communications regulators will agree is dicey. Already FCC Commissioner Kevin Martin is voicing concerns. As of Friday, Sirius carried a market capitalization of $5.2 billion. XM was valued at about $3.8 billion. Combined, the tax-free, all-stock merger has a combined enterprise value of approximately $13 billion. According to news reports, the two companies worked over the weekend to finalize a “merger of equals,” but Sirius CEO Mel Karmazen (ex-Viacom and Infinity) will run the new corp while XM chairman Gary Parsons will keep the title.