Two Phantoms as rear AV channels (bypass Dialog)

[JohnnySix]

you can have two analog to optical converters CYP AU-D4

SR preout => analog input  ® to opt converter => optical input phantom 1
SL preout => analog input (L) to opt converter => optical input phantom 2

In spark (you can configure several rooms):
room 1 : set phantom 1 on R
room 2 : set phantom 2 on L
activate optical input on both phantom
set room 1 & 2 with same volume

Can you clarify whether these instructions involve a Dialog (initially or otherwise)? I've tried allocating them to different rooms by setting them up individually without Dialog, but once they're both powered on again, Spark seems to keep resetting them to the same room and they start operating in a "mutually exclusive" manner! (If the Dialog is involved, then I don't see how they won't try to share their Optical feed with the other)