I have been studying this issue for a while. I have not made the conversion, but I think I know what needs to be done.
I have purchased the Dometic 5 button controller and have swapped the rj11 cable and got the Dometic controller to see and operate the heatpumps and the furnace. I keep the Dometic controller as a backup.
But, there is only 1 temperature sensor and it is the Dometic controller itself.
As best I can tell, the e-plex system has its own temp sensors. I know this as I have had to replace one and have it programmed with an e-plex address.
In a non-eplex motorhome, like the Mountain Aire of the same year as yours, each heat pump(HP) will have its own dometic temp (remote) sensor that run from the HP unit to a wall location. There should also be one running from the furnace controller to a wall location.
So, maintaining comfort with only 1 sensor and 4 Zones will be problematic. Somehow, you will need to install the 4 additional temp sensors.
I am on the verge of doing this sometime soon. I am planning for my e-plex to fail and I am replacing my zone 1 HP later this spring. I will install the remote temp sensor when I install the new HP.
I think the temp sensor is this one.
Harness, Wire, Thermistor Kit - Dometic 3312303.005 - Parts - Camping World
I have the following in my notes;
Newmar Remote Sensor for 2007 Mtn Aire
Keep us posted on your situation. I am very interested.
PS. Losing e-plex means you have also lost your ability to turn on/off your water pump. I have done some research in this area as well. I think I have a plan(again to make the our coach work like the Mtn Aire). Nothing easy here.