how to set up good home theater sound (and picture)


I am very new to the latest home theater formats. I have a new 4k TV but I don't yet have any devices that will stream 4K. My fios box does TV and I do netflix, amazon, and disney through our PS4. I just got a Marantz AV 7702 processor. I used to run Theta digital equipment for DVDs but no one buys disc players anymore, right (even 4k disc players)? Oppo seems to have gone out of business. Is the new PS5 an audiophile quality player? Will a new FIOS box satisfy? I'm wondering why I even have a good processor but I definitely miss good quality sound for movies. It's only OK running the current equipment into the Marantz and nowhere near what I remember from a Theta DVD player and my old Sunfire processor. It should be much better with the new sound formats. One option for video would be to run the apps directly from the TV, which would optimize video, but then I'm running an HDMI cable from the TV to the Marantz, and I assume that would be poor sound quality? How do you get audiophile quality movie sound these days? Thanks all.
dbw1
Also, does Audio Return Channel give a poor quality signal to the processor? I'm skeptical of running a high-fi audio system starting from a circuit within my television, but maybe that would be no worse than running a signal from the PS4 or Fios box?
If you’re running the HDMI out from your Fios box to the Marantz and then HDMI from the Marantz to your TV it should be fine.  I suspect you need to change some settings in both the Marantz and TV to get things looking and sounding better.  Also check your Fios cable box settings to make sure it’s sending out the highest quality signal.  If none of that works maybe you have a faulty or poor HDMI cable.  In any event, if you have a good TV and audio system things should be looking/sounding pretty good with what you have.  I’m only addressing the cable TV issue (not the PS4 streaming) to make sure that’s working right first.
What are you using for amplification? I use a Marantz 7011 receiver which is basically your 7702 processor plus a built-in 9 channel amplifier. I use Apple TV for streaming and it sounds quite good.

My Marantz system is in the same room as my reference 2 channel system and I can compare the two systems easily. Without getting too much into it, I really enjoy listening to my Marantz system when I want a change of pace from my 2 channel system.

If you have not done so already, try using the Audyssey room correction feature which should have come with your 7702 processor. It is simple to use and improved the sound quality of my HT system.

The other thing that I did that really improved the sound quality of my Marantz system was to add a pair of subwoofers. After applying Audyssey room correction, my subs seamlessly blend with the rest of my HT speakers. I get a big soundstage with solid and precise imaging with this setup. I second auxinput's sentiment that the sound is "a very refined and full sound with lots of impact."
I forgot to mention - for most music, I use the Apple TV as a Roon endpoint. Sound quality through the Marantz is surprisingly good. I also use a Squeezebox Touch with the Marantz which is even better. 
I"m using a Theta Dreadnaught II for amplification. It's a combination 2-channel/HT system and I have a separate DAC and preamp for the 2-channel (with a HT bypass, all feeding into the Dreadnaught), with a Rel Storm-III sub. I did set up with Audissey. I'll check the settings on the fios box for sure, thanks for that suggestion. I'm pretty sure at least with the PS4 it's set up properly for the best signal to the Marantz. I'm just surprised that a digital output through HDMI (all brand new cables, with 2.2, high speed and everything) from the PS4 isn't better than what I'm hearing.