I have not looked at the MDC coordinates yet as a downloadable file. Depends on the type of file they have it as. You do need a SD card as that is what your unit requires to transfer or update data on it. The file extension code will tell you what formate the coordinates are in. I just got myself some Humminbird units as well, and just got them hooked up and installed today. Have not read what file type they use yet.
I am not much help I know, I am still learning these systems myself, but there are others on here that should be a long shortly to help you out. Also try posting on the Electronics and Trollin motors thread on the main page. Ask the question there and tell them what type of file the MDC site uses and I bet you money that someone will have an answer for you very shortly. Good luck to you bud.