I'm a bit confused by the way you explained your setup below but the optimum method for making this work would be to have your PS4 connected to your HTS via HDMI then your HTS HDMI out connected to your TV's HDMI In. If that is the way you have your PS4 hooked up then you should be getting no less than 5.1 sound for most content/games. If you are only getting stereo output (L/R) then that would lead me to believe that it is something in the settings of the HTS you are using.
I would definitely not recommend having the PS4 hooked up directly to the TV via HDMI and then the Optical/ARC carrying the sound back down to your HTS as this could definitely be your issue if that is the way it's currently hooked up.
Originally Posted by NIGHTMARE_1990
Ok so I've been googling for a while but everything I can find on the issue is full of conflicting comments and suggestions.