In my case, I split the Signal right after the DAC, deliver it to the Yamaha-Receiver in my Living-Room, and to an 32 Years old Philips-Amp in my Hallway/Kitchen. After countless tries of getting the Signal through the Receiver, and from there to the Philips-Amp, which always resulted in hearable delay at the Amp, the splitting seems to be the best solution.
RuneAudio on RaspberryPI -> Behringer UCA 222 ->
Y-Splitted to:
-Yamaha RX-V473 -> Teufel Ultima 20
-Philips F4110 -> Teufel Ultima 20