The Microphone input at the receiver end of the extension can be toggled between Line and Mic mode, this is described on page 20 of the user manual as follows:
"To choose between the Line In and Microphone inputs
1 Using a USB keyboard attached to one of the USB A ports on the AdderLink XD522 receiver, press the CTRL key three times in succession. In response, the three keyboard indicators will all flash, once per second.
2 Using the numeric keys located above the main section of the keyboard (not the numeric keypad), press 3 to select Microphone The Mic icon will be displayed on screen to confirm your selection.
The second USB port on the XD522 transmitter "Link B" can be utilized by adding in a second CATX cable between the transmitter and receiver, this cable is used ONLY for the Link B USB, so is capable of supporting HighSpeed USB 2.0 devices such as USB drives, webcams etc. At the receiver, the far right hand port (B) is the other end of this link. if necesarry a USB hub may be used increase the number of devices connected to it.