by Charlie Wilmoth   The Austrian trio Radian is a post-rock/electronic group who uses both acoustic and electronic instruments. The group's members often play even their acoustic instruments in such a rhythmically precise manner that Radian sounds more like an electronic act than a band.   Radian -- which includes bassist John Norman, drummer Martin Brandlmayr, and synth player Stefan Németh -- formed in Vienna in 1996, although the group did not play its first show until a full year later. Soon after, the Rhiz label released the group's self-titled EP in Austria. The group's first full album, TG11, was released jointly by Rhiz and Mego in 2000. In 2002, Radian traveled to Chicago to record with producer John McEntire, and the Thrill Jockey label released the resulting full-length, rec.extern, later that year. Rec.extern was the first Radian release to receive widespread distribution in the U.S., and in October 2002 the group toured the Northeast and Midwest to support the album. Juxtaposition saw Radian team up with John McEntire again and was released on Thrill Jockey in August of 2004.