There are 2 groups by this name.
1) Richard Dorfmeister & Rupert Huber were both school chums and shared the same interests in music. Dorfmeister teamed up with Peter Kruder in a spam factory to form Kruder & Dorfmeister and because they never made any studio albums (the kruder and dorfmeister sessions) Dorfmeister and Huber got together to form Tosca. Their first album "Opera" was based around NYC street blues samples and deep basslines, and the tracks Fuck Dub & Chocolate Elvis spawned many remixes from the likes of Boozoo Bajou, Fila Brazillia or Baby Mammoth. Their 2000 release "Suzuki" explored the lighter side of blunted trip-hop with smooth synth textures most notably Orozco, Boss on the Boat and Ocean Beat. Dehli9 is probably Tosca's least popular album but is the first to have some real vocals. There is also a second disc containing warped piano recordings. The album J.A.C. is Tosca's more friendly album with Jazzy tracks like Heidi Bruehl & Superrob.
2) A modern Tango ensemble led by Glover Gill (active in the late 90's) in Austin, TX. The current incarnation is called GloverTango.
Tosca is an electronic music project of Richard Dorfmeister and Rupert Huber. It is Dorfmeister's second such project, the first being Kruder & Dorfmeister, started in 1994. Tosca's first album, Opera, was released in 1997 with G-Stone Recordings.