By Jeffrey Wallace / Assistant Arts & Review EditorSTS9 stands for Sound Tribe Sector 9. Based in Northern California, the electronic-jam quintet started quietly with a niche following in the late '90s, playing shows mainly in Boulder, Colo., Santa Cruz, Calif., and Atlanta, Ga. Word of mouth spread rapidly among the highly viral jam-band community, and STS9 is now considered one of the leaders in the post-Phish jam world.