Lowrance network question

I have been thinking of upgrading to a pair of LMS520’s from my current LMS332c’s. Main reason is for the ethernet capabilities, I have a Globalmap 7600HD with a ethernet port, that should tie into the LMS520’s. From what I have read, you can get sonar signal from one unit to the other with the ethernet connection or network it with the ethernet expansion unit available. My question is what is the difference between sharing the sonar signal from one unit to another over the ethernet connection or going with the broadband sounder unit which costs 3 times as much and still needs the ethernet expansion unit. Shouldn’t I be able to get the sonar signal from one of the LMS520’s go to the ethernet expansion unit and display on the other LMS520 along with the Globalmap 7600HD? Also what kind of market is there for a couple LMS332c’s?