The default volume control does not affect my receiver but using an app (Yatse) to control the Kodi app does lower and raise the volume of Kodi.
Is there a setting I can change to change the volume of Kodi with the remote control that comes with the Mi Box?
When Yatse is loaded, use the physical volume buttons on your phone or tablet.
I have no issues at all using the MiBox remote control to adjust the volume, works as is, no need to tweak Kodi.
You can get a Sideclick for your Mibox remote for $30. They have 8 programmable IR buttons.
With a harmony IR remote ($30/model 650 and above) you can change Kodi volume independently.
F8-F10 control Kodi's Mute (F8) & 'internal' volume - (F9) and + (F10) on a keyboard, if you have a keyboard connected or your remote has said feature..?