Dreaming costs nothing...., but dynamic focussing and chirp does - about 35K (USD) in this case! To match the Edgetech 4125 one would need three to four LSS-2 operated at 800 kHz. Then the image would be ok only beyond about 50 m.... No tweaking in this world can turn a "cheap" fishfinder into anything like that. Be content with your lot!
Rickard