TAS5261 grounding

Hello. I have the question about the grounding. I have four MasterKit BM 2071 masterkit.ru/.../1319305. There is one TAS5261 on each of them. I know that according to the data sheet the heat sink should be grounded. In my opinion the grounding is a connection with the ground https://en.wikipedia.org/wiki/Ground_(electricity) , but not with the common wire of all the circuit (in most cases the minus pin of the power supply). So I can't understand if it is neccessary to couple an exposed metal pad of the TAS5261 chip to the groud or to the common wire of the circuit. Should the the heat sink have an electric contact with the exposed metal pad of the chip (but not with the common wire) and be grounded? Or the metal pad should be connected with the the common wire but it shouldn't have the electric contact with the ground. Or it must 'hang in the air" at all and be very well isolated from the grounded heat sink and the common wire? Becides according to the data sheet of TAS5261 the 8th pin of the chip should be grounded. There is an electic contact with the minus pin of the power supply on the circuit. You can see it on the site above. So It is neccesary to couple the common wire of all the circuit to the ground, isn't it? I don't think it's right. I can't understand. Help me to make everything clear not to damage my amplifire. Please. Thank you.