As far as i kno if you get the LMMS unit u can network and share info from one to the other! Waiting for my new boat to arive and i have a hds 5 and an 8 plus LMMwaiting to get hooked up and I was told I would need only one card for both.
Have you looked into a tracker targa 17?? great fishing family boat.. did a lot of research and i'm switching from a legend 16 to a targa 17 go online and check the specks before u make a deision!!