Mozart’s Sinfonia concertante for violin and viola, K. 364 (320d), is his only complete surviving work in this genre. He wrote it in 1779 after returning from Paris and Mannheim .

For two decades it was known only in a few copyists’ manuscripts. The first edition did not appear until 1802. The work achieved great popularity that same year, particularly the arrangements for piano four-hands and piano trio.

This arrangement for string sextet, dating from 1808, is interesting not only for its...