We do not have anything that will do what you want off the shelf, however it is still possible. We do have one unit that does measure PH however it is only for educational purposes (DrDaq).
The only thing that I can think we can do that may be able to fulfil your requirements is the Enviromon system. The system comprises of components at the heart of the system is a data logger, the EL005 this is initially configured on the PC and then can be left to run remotely (or remain connected to the PC) to collect data and then connected back to the PC to download the data.
Connected to the data logger you can have up to 10 converters, each of these converters has a different purpose and can measure, temperature, voltage, current and so on. In your case I would recommend the EL037 general purpose Voltage/Current converter, this uses the standard, 4-20mA, +/-2.5V or +/-10V inputs for use with sensors, you can then use a scaling file with the software to show the readings in the units you require.
I do not know if there are transducers out there that give a pH reading as a current or voltage, however this is something you would have to find out yourself.
The relays can be handled by one of our alarm converters, the EL042 which has 3 relays that can be set on an alarm condition.
In terms of the IP66 casing, our devices to do not have these ratings, however I do not see any reason why you cannot have our devices in a standard IP66 case.
In terms of the distance the converters can be hundreds of meters away from the main logger.
Hope this helps.