I would suggest that you look into a NMEA2000 compatable plotter. I don't believe the SH units are, still old NMEA0183. NMEA200 makes installation and addition of components down the road much much easier.
Here is a list of certified product from the mnea2000 website
http://www.nmea.org/about/news.cgi?article_id=177
Hereis a easy to read explanation of the system
http://www.lowrance.com/Products/Marine/LowranceNet/LowranceNet_sample.asp
I installed the Lowrance 6600HD plotter with fuel flow sensors in addition to an LMF400 display. Works great, I'm very pleased with the hardware and NMEA2000
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Jvalich
http://www.badcock.com'04 FW 288 Vista "Mental Floss"