I've just set my remote play up and it was a bit laggy at 1st then then picture caught up.
Then i realised that the sound was coming through.
But now its working...
I think that when i switched my tv to the ps4 just to look at the settings and was like derhhh its on the pc screen.
I flicked back to the pc and it started working.
Strange.. I know. but it probably didnt sync correctly and still wanted to be a real ps4.
I hope you can take something useful from this lol.
GD luck. 