Voices heard, then not heard. This is weird and seems unsolvable.

Both good suggestions. Thanks to MASQ and Kimputer. One thing I did notice is that the wires to the center channel can be attached to low, medium and high.

But, it seems as though it would be one of the things above given it comes and goes. It's strange, again, because when I wasn't really paying attention I thought it was normal voices then no voice, but it is really normal voices and really low voices. Such that a normal voice is a 10 out of 10, the other voices are 1.5 out of 10. Weird that it comes and goes.

As the whole system years ago was set up by Circuit City, I have often wondered if everything was set up correctly. Yuk! But, probably better than I although nothing but an octupus of wires back there. It seems to be 5.1, although I can change to 5.1.

Streaming, whether through Oppo (damn, paid $1,000 for that DVD player about a day before DVD became old news), but still a smart component, but now via nVidia Shield Pro via the Marantz.

It's your center speakers in the surround system.  I woulld run a test suite

How would I run a test suite?

Did you play the link I provided yet?

I read it. I am not at home yet. I will definitely go through it. Still weird that it comes and goes. It is not like there is very high music coming from the two tower speakers and then not.

I wonder if it is just a bad center speaker? Also could connections to the low be changed to medium. Maybe the connections are bad? Not to doubt you. Just wondering.

Without being there at this very moment, I am rather certain, it is at the same place each time.

I tried to back and troubleshoot The Sopranos, but it is now on HBO Max, a mere $19.00 a month. No thanks. I mean with a million streaming choices, why would I want to pay almost $20 a month for one channel. I remember 40 years ago as a college student with cable, subscribing to HBO and Cinemax. You would get a little pamphlet mailed to you with all of the movies listed and their times. You ACTUALLY had to make sure you were in front of the television at that time. I mention college student, because at that time making the decision to subscribe to HBO, Showtime or Cinemax was a huge deal.

Sorry, but I digress.

These are all very helpful. I am not sure which solution to choose because of what seemed to fix it. As stated earlier the center speaker has connections for low, medium and high. The output cables from the receiver were connected to the low (as I am rather certain since I live alone and didn't change them) they have always been. I changed them to the mid connectors and everything is fine. ?

Good that it's fixed, as it's unlikely the Video Streaming Fairy visited your place and changed the wiring I guess one of two things changed, either your old connection to "Low"  was somehow broken and wiggling the wires into medium have restored the connection or the balance on the the stream changed and neither nVidia or Marantz were able to recognize or compensate for that.

In any event, you can now enjoy your TV and we were all right :)

If you want to digress - as a kid I had a choice of a maximum of two channels in black and white which went off the air at midnight and came back on at 7am!

LOL. I will do as you suggested. I lived in Florida with the antennas on the room (luckily flat roofs there). And tin foil on the rabbit ears. And taking the entire TV to Reid's TV to have it fixed.

So, can one choose more than one "Yes! This is my solution? Or do I have to choose one, then use the "No, but it is helpful?"
 

I am wondering if it is time to upgrade some of my components. They are all pretty top of the line, but they have been there for around 15 years. The Marantz looks like it has never been touched.
I purchased all Definitive speakers but, while they are very good, I don't like them overall.
Aside from this, I just can't seem to get the electricity to be completely clean even with appliances made specifically for that.
Of course, everything would likely be HDMI or some other connection rather than simply cable with twisted copper cables  being inserted into the speakers.

By the way, I would like to try https://www2.iis.fraunhofer.de/AAC/multichannel.html, but I am not sure how to run that on the system. Do I bring up a browser? Do I use a laptop. Sorry, rather dumb here.

Regressing again: By the way, if I purchase a new 4K TV, does it have to be a smart TV, if I already have nVidia and/or Roku for streaming and applications.
And, even though the speakers are set up for 7.1, the receiver doesn't seem to be compatible with that. Sorry if this is an entirely different question, just thought with some new components, it would handle most of the center channel problems, not that I would upgrade just to fix that. Or make it better.

Depends how your speakers were set up. If your current viewing device (where you watched the videos on that didn't have the correct sound) doesn't have a browser, you need to use a PC or laptop, and temporarily move the sound cable to that as well.

Might still remain a puzzle why this only started manifesting itself a month ago though with no change at the receiving end.

Should we blame the New Jersey mob as they were mixed up in the start of it?!

LOL. Agreed! In fact, it is the Sopranos. And, soprano would be at the highest level of the four singing voices. Not exactly what you would want going to the low.

https://www.experts-exchange.com/questions/29218652/Voices-heard-then-not-heard-This-is-weird-and-seems-unsolvable.html#a43304644 

Thanks! Just to be clear though, I have never touched anything on the receiver, speakers, etc. until I moved the wires from the low connection on the center speaker to the middle connection of the center speakers.

It was Circuit City who set it up. Granted that confirms your statement that the receiver is only for pros. I wouldn't call them pros.

I live in a relatively small city in Maine and, therefore, we do not have any professional HT installers until you get to Portland. But, that may be the route I need to go if necessary.

You also wouldn't notice it if you watched stereo audio content all that time. Only when you start watching mixed 5.1 or 7.1 audio content will the problem present.
Stereo would've mixed center dialogue to BOTH speaker at about half the audio volume. You would easily still hear it.
Then you go to 5.1 or 7.1, now the dialogue is mixed only to the center speaker. Correctly connected speakers would still hear it center, but you use normal speakers on the sub woofer connection and would always hear muffled sounds for center dialogue.

Hi experts,

I remember the time that I had to go through the answers and pick one and then assign points to those that helped. While this method is much easier, I get confused as to how to do it correctly. Up until my last few questions, I have picked a "Yes! This is my solution," then use the No, but it is helpful. But, some expert told me I can actually choose more than one Yes, this is my solution.

The other difficulty is where an expert may post an answer and more than one solved the problem. Many have helped here, although Kimputer has not only stayed with the question the longest and given much more information and provided answers that were helpful, there are others that have helped as well.

I SUPPOSE WHAT I AM ASKING (sorry for the all caps) is advice or rules as to how I am to 'grade' questions when it is completely done.

Try this
https://www.experts-exchange.com/articles/27319/How-do-I-accept-multiple-comments-as-my-solution.html

Well, it is working now. I suppose I have a lot more to do to get it to sound the way I want. 

Thanks. Sorry everyone. I didn't even know I hadn't closed the question. Wish we could go back to the old way. It was a pain at times but it made more sense to me.