Mannosyltransferase involved in outer chain elongation of asparagine-linked oligosaccharides of the type Man(9)GlcNAc(2). May otherwise add the first alpha-1,6-mannose to the Man(8)GlcNAc(2) core oligosaccharide from the ER. Represents the first enzymatic event required for synthesis of outer chain mannose linkages on yeast secretory proteins. Transfers an alpha-D-mannosyl residue from GDP-mannose into lipid-linked oligosaccharide, forming an alpha-(1->6)-D-mannosyl-D-mannose linkage. Is recycled between the trans-Golgi network and a late compartment of the endoplasmic reticulum. The conserved DXD motif is involved in enzyme activity. Belongs to the glycosyltransferase 32 family.