Thanks MI77915 for asking the question. It has been asked before, but as time moves on, so does equipment and reliability so my view is it is always worth asking again.
I have an IROX PRO-X which has been marketed under various brand names as Hideki, Mebus, TE923, and like yours after 6 to 7 years, I am having trouble with sensors. Some are no longer available (UV) and some have been replaced once already (Rain). Even though I did the "Mod" adding an external antenna, the reception of the signal from the 1st sensor is and has always been a little off.
I am thinking about updating. The Davis equipment is a "Rolls Royce" product, but in Europe the cost is 3 or 4 times the price of other systems and I can't justify it. Also service in Europe is not as good as the US - $30 upfront before they will even look at a unit, then costs for everything.
Like you I want a modular system. I have four outdoor sensors, the master, one in a greenhouse, one in an orchard, a soil thermo, raingauge and until it broke the UV.
Please keep posting your research, as there a lot of units out there. I live in a USDA zone 10A part of Europe, so it is the baking heat of summer which causes problems. Last winter there were just two nights when the ambient temp fell below ZeroC/32F.
It would be nice to find something which would last more than 6/7 years but that seems to be the built in obsolescence of electronics.
NW