Hoping I can find a definitive answer to an Opentherm setup query.

I have just had a brand new wet central heating system installed from scratch, here are the setup details:

S-Plan configuration
ATAG 24kw SI system Boiler
200L unvented cylinder
2 zones configured (HW/CH), each with a Honeywell 2 port valve
Currently have 2 x BDR91s controlling the HW and CH zones
12 rads, 11 with HR92s, 1 without (bypass rad)

The system is working as expected (albeit fine tuning is required on the timings/set-point side). I have the iPhone app, and can control the CH/HW remotely. I had a ghost zone on my iPhone which Iíve now had removed thanks to another thread on this forum.

I have found the Opentherm installation instructions online, looks clear enough, my query (forgive me, Iím a novice to this world), is how it should be implemented to my new system?

Iíve read threads about not needing a BDR91, but why not? And which one (CH or HW?). If not required, how should that zone be setup both physically and electronically?

Would be very grateful if one of the experts on this forum could please advise steps I need to take, to successfully implement Opentherm. I want my brand new central heating system to be operating at optimum efficiency, but I canít find a clear step by step set of guidelines as to how OT should be implemented.

Thanks in advance, looking forward to some solid guidance!