[MARMAM] Hydrophone use for increasing sightability

Hello- We are in the process of looking at hydrophones as a means of increasing our sightability in less than ideal conditions. We are not, however, necessarily looking to record. The primary species involved are the bottlenose and Atlantic spotted dolphins. To give ourselves a bit of directionalilty, and to reduce cost, we are open to using two omni-directional hydrophones hooked up to stereo headphones. We are looking for suggestions on setup, hydrophone manufacturers, and a "recording" device so that we can hear the received signal. Does anyone have any suggestions on any of these fronts? Please respond off list to tmcconch@gmu.edu. Thanks for your time.