The real question is: Is the black connector on the Power Amplifier (PAMP) connected electrically to the black lead of a VP-BTA ?
The answer is yes. This is true whether you are using the Power Amplifier and VP-BTA connected to a LabQuest (via the audio cable) or connected to a LabPro (via the double BTA cable). This would be one more reason to use DVP-BTA in electrical experimenting.
Our engineers also remind us that if you are using the current sensing aspect of the Power Amplifer, the current measured will be the sum of all current that flows through the black connector of the PAMP. There is a 0.1-ohm sensing resistor connected to that terminal.