I upgraded my Ultrascan PC in October 2012 as the old unit could not communicate with modern serial ports. It only worked on Windows XP and older. I tried pretty hard to resolve the issue, and Cory from Interphase was most helpful but they were aware of the issue and had not found a solution either.
For the upgrade I dealt with the old Interphase office, which by then had just been renamed "Garmin Santa Cruz". Due to refit delays I only installed and tested the unit in April 2013. There was an issue requiring the unit to be returned, and the RMA address was in Kansas. The Garmin support was quite efficient, but IIRC by then the Santa Cruz office phones had been disconnected and the office presumably closed. Perhaps the key Interphase folks did not want to relocate and left for other pursuits? It is a niche product, so without the original Interphase tech people Garmin could well have had difficulty with further product development.
My warranty return was surprising - the replacement box would not work either. It turns out the original power cable that was supplied had the wrong polarity! Easy fix, but not something obvious to track down.
I have not used the Ultrascan very much and there is an art in reading/interpreting it, although its not that difficult really. As with many things, practice! I expect it will get a really good workout next cruising season as I enter coral lagoons.