I can confirm Dawntreaders posting as correct having done the same upgrade myself, albeit to a Raymarine A77 chart plotter, and all my ST60 instruments including the autopilot continue to converse with each other. Additionally I can control the autopilot from the chart plotter if I choose to do so.
Salty, I am about to implement this upgrade. One question: does the SeaTalk convertor need a separate 12v supply or is the power to the individual instruments sufficient?