Catalysis of the reaction: dTDP-L-dihydrostreptose + streptidine 6-phosphate = O-(1->4)-alpha-L-dihydrostreptosyl-streptidine 6-phosphate + dTDP + H+.
thymidine diphosphodihydrostreptose-streptidine 6-phosphate dihydrostreptosyltransferase activity