STS9 has announced some additions to its summer tour. On August 28, Outkast’s Big Boi will join a bill at the Verizon Wireless Amphitheatre in Alpharetta, GA that also includes previously-announced appearances by the Disco Biscuits, Big Gigantic and John Hughes. But wait, there’s more…Mos Def also has signed on for the Georgia date. This is one of two shows, where he has been added to the bill, as he also will open for STS9 at Chicago’s Aragon Ballroom on August 21. In addition, two official After Parties have been announced, with members of STS9 joined by Big Gigantic at New York’s Irving Plaza after the Roseland show on August 12 and at Philadelphia’s TLA after the Penn’s Landing date on August 14.