I really hate to have to agree with Robbo... But, in this case I have no choice...
At any rate 'brd, think of that 50/200 kHz transducer as you would speakers of a high-end stereo system: the better the speakers, the sweeter the music!
You can have a great system, but with a poor or incorrectly installed transducer you will not get a very good picture.
Check out
http://www.Airmartechnology.com for the full line of high end "speakers" for your "underwater stereo"!