Don - I am not sure if you are permanent in Asia or if you are coming back with the boat to N/A as that might have some bearing on what autopilot you choose. There are several big guns in this business besides the manufacturers such as RayNav etc. Two of the most common autopilot firms in the North West are both in Vancouver BC. They are AutoNav and Comnav. Both firms have an excellent reputation and have world wide reps.
If you go to the Comnav site and pull up the autopilot section you can work through what / how / why of a system. The dotted lines show what else besides the basic system can be added.
I believe that either companies systems can be slaved into a hydraulic power steering system by using a set of solenoid valves in place of the reffered to "pumpset" as all it does is provide pressurized hydraulic fluid to the steering ram that in your case already gets it from your power steering pump.
I have a ComNav 1001 system that is very common on commercial craft in this area and has worked great for many years.
Let me know if you want any further info on either of these system as I know the people at both firms.
John Tones "Penta"