I have been using Pluto TV on my Sony 4k TV but the sound seems low. Do some internet streaming APPS only have mono sound? Or does having a streaming device with an HDMI cable have better sound? Thanks.
It isn't typically the apps (apps being software applications) that are the problem. Perhaps half of the streaming services
only send a stereo signal. This includes Pluto and Fubo (on their live content). Pluto's audio downconversions are spectacularly poor. Turning off any simulated surround sound processing can help quite a bit.
I think Hulu may be an exception as they don't have full audio support in some of their device apps.
This is one of the things that you don't find out about a service until you try it and why trials are so important. Such is not to say that these services won't ultimately send the full audio quality of the original work but for now, they aren't.