It seems to me that if you need to generate large acoustic signals underwater, HASEL actuators might be the way to go.[1] Since they're effectively just bags full of incompressible fluid, they could work at any depth.

Sensing sound.... that might be harder. Perhaps you could close-loop control the capacitance of the above, and "listen" to the error signal?

[1] https://www.artimusrobotics.com/