When violinist William Fedkenheuer steps onto the stage this month with his colleagues in the Austin-based Miró Quartet for a series of six concerts at the Butler School of Music at UT-Austin (Sept. 6-8 & 27-29), he will achieve a distinction that few other professionals can claim. He will be one of the few living violinists who have performed all sixteen of Ludwig van Beethoven's string quartets for two violins, viola and cello as both a first and second violinist.