N-acetyl-alpha-neuraminosyl-(2->3)-beta-D-galactosyl-(1->3)-N-acetyl-D-galactosamine + CMP-N-acetyl-beta-neuraminate = N-acetyl-alpha-neuraminosyl-(2->3)-beta-D-galactosyl-(1->3)-[N-acetyl-alpha-neuraminosyl-(2->6)]-N-acetyl-D-galactosamine + CMP + H(+) — reaction