Duplex was originally a c64 demo and cracking group, formed in 1989.
Swapper advert in Cracker Journal 19 (march 1990) said, "DUPLEX, THE FAMOUS C64-GROUP STARTS RUNNING AND RULING ON AMIGA!!", and listing a PLK in Pinneberg, Germany for contact. The new section made similar observations.
The group disbanded in 1991, according to CSDB.