A method for improving multiple-user (MU) multiple-input-multiple-output (MIMO) protocol efficiency includes transmitting an MU frame to multiple devices. The MU frame is beamformed to enable a corresponding one of the devices to receive an intended stream at high power. The MU frame includes an additional sounding-field. Acknowledgement (ACK) responses are received from at least some of the plurality of devices. Each of the ACK responses includes a sounding response frame including a channel feedback.