Catalyzes the reduction of the macrocycle of precorrin-6X into precorrin-6Y. NADP(+) + precorrin-6B = 2 H(+) + NADPH + precorrin-6A Cofactor biosynthesis; adenosylcobalamin biosynthesis; cob(II)yrinate a,c-diamide from precorrin-2 (aerobic route): step 6/10. Belongs to the precorrin-6x reductase family. Was originally thought to originate from Pseudomonas denitrificans, but similarity searches show that the sequence is much closer to Sinorhizobium. The entry's taxonomy has been changed. Originally thought to be encoded on the other DNA strand, the correct open reading frame was subsequently identified.