To the OP, have a look at Roon as it may have the features you are looking for although at a cost.

https://help.roonlabs.com/portal/en/kb/articles/dsp-engine

I have not read the whole thread but to the OP… look at Roon it may do what you want with Sonos although at a cost.

https://help.roonlabs.com/portal/en/kb/articles/dsp-engine

@John B

Sonos is not a charity for the benefit of persons who self-identify as audiophiles. Sonos presumably includes features that enough Average Joes will value and use.

What you regard as 'basic functionality' is something I regard as useless at best. Let's just agree to differ. 

John, your opinion may not reflect the opinion of the general public. I'm sure if Sonos would do a poll on their official page indicating that they would like to add new features to personalize their sound, I'm sure many would be delighted and the votes would tilt in my favor. We can not just trust the opinion of the same 5 people who take stubbornly pleasure against my idea since the beginning of this post.

Sonos is not a charity for the benefit of persons who self-identify as audiophiles.

I do not agree those who are willing to pay 3k and more for a setup are those who appreciate music beyond the general average. I hope potential Sonos customers won't read this.

Erm...neither does yours though you claim that here at the end of the quoted sentence by speaking for all people, while John does not do so for his opinion:

having a 3 choice of adjustment is NORMALLY the basis of things as in all the other daily devices that I use and that all people use 

And I do hope that potential Sonos customers read the entire thread so those that want the jazz that you do, do not buy Sonos.

Full marks to you for tenacity, though 

@Kumar

so those that want the jazz that you do

Sad to find that asking for an additional sound option is considered jazz for you.

Full marks to you for tenacity, though 

I send you back the compliment, for my part, I just bring an idea, but sad to see that when the idea does not go in the same direction of the leaders of the forum like you then you think that you are going to shut up people. Unfortunately, you haven't found the right guy.

I am no leader and I never claim that the universe endorses all I say, but talk away... ..it may make up for not having the third slider.

First time posting! I think an equalizer would be a great addition. Everyone has personal preferences to how they like to hear their music. If you like music flat & as it comes from the recording studio then great don’t bother using the tone controls/equalizer and if it sounds better (to you) after you’ve done some tone adjustments then that's just as good. Surely its all about choice and this is (I would have thought) a relatively simple addition that would enhance the flexibility of the system.

Couldn’t the OP just use the existing bass and treble sliders to reduce those frequencies, thereby increasing the midrange in comparison?

He could, if he was not so hung up on having a mid range slider just because his car has it.

Audiophiles - The Port needs to be bit-perfect or it’s useless to us audiophiles!

Also audiophiles - We need a 10+ band equalizer to tailor the sound to our preferences!

The direct opposite to the above lot are the audiophiles that disdain even the presence of tone controls on their preamps/amps because even when flat, the associated circuitry “corrupts” the virgin signal. So some amps even have a defeat switch to take that circuitry out of the signal path. A switch that is corruption free?

There are all kinds of audiophiles down the rabbit hole that they live in. They do serve a useful purpose though - their compulsive upgrading keeps up the supply side of the consequently excellent value used HiFi kit market.