Oh my. I actually used something kind of like the third one (array of buttons for each volume level).

I wanted something more convenient than the Denon app for changing inputs and volume on my Denon A/V receiver, poked around a bit and found that the receiver has an HTTP API that the app uses, and decided to make a simple web page that could use that API. I could then add that to favorites in Safari and then control the receiver from the browser.

Here it is: https://imgur.com/a/ExkhOgO