Not sure what tube mic you're using, but the box that the mic connects to with the 7 pin connector is the power supply for the mic, not a preamp. The 3 pin connector coming out of that box is the raw mic signal. Put the pad here between the power supply and the interface/preamp.
The reason for the 7 pins from the box to the tube mic is 3 pins for the audio signal, and 4 pins for the voltage that the tube needs to operate.