GO:0050659:   N-acetylgalactosamine 4-sulfate 6-O-sulfotransferase activity
Catalysis of the reactions: 3"-phosphoadenylyl sulfate + dermatan = adenosine 3",5"-bisphosphate + dermatan 6"-sulfate and 3"-phosphoadenylyl sulfate + chondroitin = adenosine 3",5"-bisphosphate + chondroitin 6"-sulfate.