Catalyzes the conversion of 6-deoxyerythronolide B (6-DEB) to erythronolide B (EB) by the insertion of an oxygen at the 6S position of 6-DEB. Requires the participation of a ferredoxin and a ferredoxin reductase for the transfer of electrons from NADPH to the monooxygenase. 6-deoxyerythronolide B + 2 H(+) + O2 + 2 reduced [2Fe-2S]-[ferredoxin] = erythronolide B + H2O + 2 oxidized [2Fe-2S]-[ferredoxin] Antibiotic biosynthesis; erythromycin biosynthesis. Gene disruption leads to the accumulation of 6-deoxyerythromycin A, an antibiotic with increased stability at low pH. The bound substrate forms no direct hydrogen bonds with the protein. Belongs to the cytochrome P450 family.