Put the big screen at the dash to help with your side scanning and searching. You can have them both run the same Side Scan transducer off the LSS box. However, Lowrance uses two transducers then, you have the one just for Side Scan and Down Scan, and another one for 2d sonar like your 5 has. I recommend mounting the new transducer to your TM and use that transducer for the 5 and the one on the back for the 7 at the dash. Then have them share the Side Scan/Down Scan transducer with the Ethernet connection.