Why do I have 2 receivers??

I hope someone can help,
We have a Mitsubishi ground source heat pump system with a water cylinder with a Mitsubishi PAC-IF013B-E Unit on the front.
Downstairs we have a wireless Danfoss TP500Si thermostat which talks to the Danfoss RX1 single channel receiver also attached to the unit.
There is also a Mitsubishi PAR-W21MAA which seems to communicate with everything else.
But there is also a Danfoss FP715 SI.
The whole system is very temperamental, in winter when the heating was on we seemed to always have hot water, but now in the summer when the heating is off, the hot water is very temperamental.
Long story short, i have bought a Hive complete system with hub, receiver and thermostat.
But now I am uncertain which piece of kit is replaced with the hive receiver. I'm even thinking now that I might have bought the wrong one.
I have bought a dual zone because I thought it was a simple matter of replacing the FP715 SI which is a dual zone. But now I'm at a loss.
My question is: with my setup, how would I connect a hive to it. Any other advice would be great.