I converted my 798HD SI for ice fishing last winter. To do this with your unit you will need to buy the following items:
PTC-U-NB (no battery)
PTC-U comes with battery
These are the soft cases with the mount and everything is included. assemble and plug your unit onto the mount.
for a transducer you will need an
XI-9-20
These are humminbird part numbers. If you google you can find deals on them online. I purchased mine off ebay.
The only other thing you need to do before you hit the ice is set the unit up so that it will recognize the ice transducer. To do this all you have to do is turn off your simulation mode in the menu and turn on your ice fishing mode. Jason Halfen has a video on youtube to show you how to do it.
I love my unit on the ice the only thing I would change is the shallow water read capability once you get into 10 feet or less of water these units have a high RMS wattage and in shallow water you need to turn your sensitivity way down to be able to read your graph properly. Anything 10ft and deeper though. Game on!
Best of luck to you this ice fishing season!
Tom