My PS4 is connected to HDMI3 input on Super4 X55, and my Pioneer AVR is on HDMI1 with ARC enabled. Sound from PS4 passes through, but it is only stereo. I have tried all possible configuration and settings on PS4, AVR and the TV, but could never get it to output 5.1 surround, unless I connect PS4 directly to AVR.
I have just installed FireStick, and I cannot get 5.1 surround sound out of it. So it seems that no of the devices (PS4 and FireStick) connected to HDMI produce 5.1 surround sound, while they do if I connect those directly to my AVR. Over-the-Air channels have no problem sending surround sound. I have tried HDMI ARC and optical cable.