I don't know how to remove all sounds for the Roboport with this mod.
I had to use VolumeControl to remove the roboport-open and roboport-close sounds. Roboport option in your mod does not do this.
I was able to update VolumeControl mod with changing this line in info.json to: "factorio_version" : "2.0",

Right! The open/close sounds of entities actually fall outside the scope of my mod; it's only meant to muffle the constant working or idle sounds of entities, which, by far, are potentially the most annoying to me.

Of course, Volume Control targets all uses of a particular sound file, which is sometimes undesired, so I probably won't implement its functionality into my own mod. (I also have doubts about the way it searches and modifies the database).

That being said, I am still looking to improve my mod in various ways when I have the time and energy for it, and adding settings for open/close sounds is something I could consider. Are there any other sounds that you wish you could silence or reduce the volume of? Please do let me know!

Thanks. Following is what I currently have adjusted in the Volume Control mod.
"{base/sound/radar.ogg, 0.3}," .. -- there is a mod for this Silent Radar mod.
"{base/sound/pipe.ogg, 0.2}," ..
"{base/sound/pipe-to-ground.ogg, 0.2}," ..

  "{__core__/sound/wire-pickup.ogg, 0}," ..
  "{__core__/sound/wire-disconnect.ogg, 0}," ..
  "{__core__/sound/wire-connect-pole.ogg, 0}," ..


  "{__core__/sound/clear-cursor.ogg, 0}," ..
  "{__core__/sound/list-box-click.ogg, 0}," ..
  "{__core__/sound/rotate-big.ogg, 0}," ..
  "{__core__/sound/rotate-medium.ogg, 0}," ..
  "{__core__/sound/rotate-small.ogg, 0}," ..
  "{__core__/sound/smart-pipette.ogg, 0.2}," ..
  "{__core__/sound/undo.ogg, 0.2}," ..

  "{__core__/sound/deconstruct-bricks.ogg, 0.2}," ..
  "{__core__/sound/deconstruct-large.ogg, 0}," ..
  "{__core__/sound/deconstruct-medium.ogg, 0}," ..
  "{__core__/sound/deconstruct-small.ogg, 0}," ..
  "{__core__/sound/deconstruct-select-start.ogg, 0}," ..
  "{__core__/sound/deconstruct-select-end.ogg, 0}," ..
  "{__core__/sound/delete-item.ogg, 0.2}," ..

  "{__base__/sound/lab.ogg, 0.5}," ..
  "{__base__/sound/roboport-working.ogg, 0.1}," ..
  "{__base__/sound/open-close/roboport-open.ogg, 0}," ..
  "{__base__/sound/open-close/roboport-close.ogg, 0}," ..
  "{__base__/sound/roboport-door.ogg, 0}," ..
  "{__base__/sound/roboport-door-close.ogg, 0}," ..
  "{__base__/sound/item/roboport-inventory-pickup.ogg, 0}," ..
  "{__base__/sound/item/roboport-inventory-move.ogg, 0}," ..

  "{__base__/sound/heat-pipe.ogg, 0}," ..
  "{__base__/sound/substation.ogg, 0}," ..
  "{__base__/sound/accumulator-idle.ogg, 0.5}," ..
  "{__base__/sound/accumulator-working.ogg, 0.7}," --..

All right. It will probably take a lot of work to allow for modification of all of these, so I am not too keen on that yet, but I have just created a fairly quick fix and uploaded it to the portal! To be specific, I have uploaded v2.1.0 for Factorio 2.1, along with v1.2.0, a backport for 2.0. Be sure to read the changelog.

Long story short, some entities rely on special sound categories, but I have now made another prefix modifier, "o", available in the settings, which changes them collectively. As an example, to disable just the normal working sound and the door open/close sounds of the roboport, you may write "ao:roboport" (or in this case just "roboport", since it has no idle sound category).

I misunderstood what you were talking about when you said that the open/close sounds could not be removed (I thought you were referring to the gui), but this update should address the problem you were having. Let me know if it works!

Just uploaded new version with updated description of settings, v2.1.1 (2.1) and v1.2.1 (2.0).

Thanks.
Works great. These are my settings:
transport-belt,underground-belt,splitter,25:pipe,25:pipe-to-ground,25:storage-tank,electric-pole,accumulator,radar,beacon,roboport,heat-pipe,construction-robot,logistic-robot,25:assembling-machine,50:lab

50:heating-tower,a:agricultural-tower,50:pump,valves-one_way,valves-top_up,valves-overflow

And I decided that I don't need the changes to sounds in Core as shown above.
Volume Control mod is no longer needed for me. Also the mods with 'Silent' in the name no longer needed.

Wonderful! And thank you for the detailed response on how the mod meets your current needs. (I think it's funny that your settings are very similar to my own! XD Perhaps it's the same sounds that tend to be disliked...)

I'll take my time now to think about whether there is anything else I want my mod to do. As always, feedback is welcome.