Pacific Investment Management Co., the world's biggest active bond manager, with $1.59 trillion in firmwide regulatory assets under management as of March 2015, sent shock waves down Wall Street in September 2014 when legendary CIO William Gross abruptly left the firm to join Janus Capital Group. While shares of Janus rocketed 43 percent on the news, PIMCO has endured heavy outflows. Firmwide capital dropped from $15.62 billion to $14.69 billion, driven primarily by investor withdrawals. The bond king, as Gross is known, had managed most of the PIMCO's assets, including the then-$221.6 billion Total Return Fund, and helped transform the California firm into a nearly $2 trillion business. Investor withdrawals overshadow the remarkable gains Gross's replacements have made since his departure…