HI there

This issue is a PS4 issue im afraid - unlike the PS3, the PS4 does not give options to force whichever speaker pattern you like (i.e. 2.0, 2.1 etc) - However there is a work-around to force the audio to stereo.

Note: Keep the HDMI connected to the TV from the PS4 - no need for other cables

1. On the PS4 goto Settings > Sound and Screen > Audio Output Settings
2. Change the Primary Output Port to "Digital Out (Optical)"
3. It will then display Audio Options - Uncheck Dolby Digital 5.1ch, DTS 5.1ch, AAC and ensure that Linear PCM is checked - then click [OK]
4. Change the Audio Format (Priority) to - Bitstream (Dolby)
5. Done

You should now be receiving 2 channel stereo - I have tested this on my PS4, connected via HDMI cable to an AV Reciever - the AV Receiver is telling me its 2ch Stereo.

Cheers