I can’t begin to express how happy it would make me if the volume buttons on the side of my iPhone would adjust the volume of the active zone in Roon. 
After years of using this method to adjust volume in Airplay, Chromecast, and Spotify Connect, I’ve grown quite fond of it. It always surprises me when it doesn’t work in Roon.
+1 for this idea it would be great to have on my iPhone.
I agree, it’s wonderful.
I have it, when I plug my Audeze headphones into the iPad using Audeze’s Lightning cable/DAC/amp.
It gives integrated volume control through the iPad hardware buttons, and the Audeze cable-dongle physical buttons, and the Roon slider, and they all work together.
The only disadvantage: Audeze and Roon achieve this because the audio goes through the iPad software stack, which is limited to 48k.
But I happily take this, because it’s so slick.
Even though a USB attached DAC can play high res.
Apple only allows App developers (as an exception) to use the volume buttons to take photos and not for other features.
2.5.9 Apps that alter or disable the functions of standard switches, such as the Volume Up/Down and Ring/Silent switches, or other native user interface elements or behaviors will be rejected.
https://developer.apple.com/app-store/review/guidelines/
I think using the buttons for remote control can only be used in Apps distributed outside the App Store (side loading). As such Apps have limited lifetime it’s not very practicable.
I’m not asking for the function to be altered. I’m asking for the volume buttons to work as volume buttons, exactly as they do in at least three other instances:
In the case of AirPlay, it’s a native Apple thing, and the stream goes through the mobile device, but it does control the volume of the endpoint itself.
With Chromecast, it’s a direct competitor to Apple, the stream doesn’t go through the device, and yet the volume buttons still control the volume of the endpoint itself. Same with Spotify connect.
+1 for hardware volume buttons on all remotes.
I only know AirPlay. Are you really sure that the iOS device does not process the audio? Can you play audio on the iOS device independently from the Chromecast or Spotify? If it’s possible, what happens if you control the volume? And what is showing up in the lock screen widget for playback control?
For my use case I‘m very happy that the volume buttons on iDevices do not work for Roon. I have for my Devialet Phantom system Spark running in the background, which enables iDevices buttons to control the volume. Unless Devialet in the future decides to implement RAAT in the Phantom system it is better that Roon, which runs in the foreground does not take over my HW volume control. I use Roons volume control to fine tune the volume (control of the RPi volume) und the coarse button control that has a step size of 6% per press as ‚gain control‘ of the Phantoms.
P.S.: Of course I would not be against a user configuration of the HW buttons, but it‘s not Roon philosophy to offer many tunable parameters.
Yes, I’m certain the iOS device is not processing the audio stream on Chromecast and Spotify Connect. You can turn off the iOS device and the stream will continue uninterrupted. I can’t test it just now because I’ve abandoned both in favor of roon, but I believe that the hardware buttons only control volume on the most recently used App.
I asked for this in 2016 already…
A lot of +1’s on that thread too!
Even if roon implements a crude hardware volume control with 6% steps, you could still use the software buttons within roon for finer control. Same function, but without requiring a second app (and it would work for all types of endpoints).
But yes, making it a configurable option would be a fine way to do it.
I can name a few apps off the top of my head that this works in. The best implementation is in DS Audio. There are work arounds to apples rules.
I think it works in BluSound’s and Sonos’s apps.
I asked for the same thing a few months ago! Lots of apps use the volume buttons for volume, including the Harmony remote software which remaps the volume buttons on the iPhone to the volume buttons for whatever receiver you are using in the app. I see no reason why Roon couldn’t do this. It’s a much requested feature!!
Another +1 here. As said it works perfectly in both bluesound’s app and sonos’. It’s the missing link in usability for me, the on screen control is too fiddly and too many clicks away for something which is used so often.
+1. A few threads on the same topic… done deal I’d say 
FYI, the Sonos app does allow volume control with the volume buttons in iOS and on occasion it will work from the Apple Watch too. Plus skip forward and back with onscreen control while the phone is locked.
+1 Please enable this. So much more intuitive for volume control. Simple Control (formerly Roomie) and Sonos both allow for this.
Using roon ios app on my ipad I can increase and decrease volume of music playing with the buttons on the ipad. The same applies for my iphone.