You are sampling the voltage of 2 signals.
The signals are linear sound pressure waves that superposition applies to, and the pressure (more specifically the force) is directly proportional to the voltage created by the transducer. Velocity of the transducer vibration is proportional to the current. This is based on the electroacoustic reciprocity principle.
[itex]\frac{V}{v} = \frac{F}{I}[/itex]
The force times its velocity will be the power, not just the force you measured, which is what your voltage data represents.
Since you are not measuring voltage AND current of your signal, you can only know what the relative force/pressure is, not the power. So it makes sense to add with the units that you measured are in  volts.
All of your other concerns about power, coherence, etc. are besides the fact that your signal is in volts, and those other factors depend on spatial, time, and transducer variables that will give you the expected power from the volts you use.
