Two Phantoms as rear AV channels (bypass Dialog)

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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