Priority of the Nougat sound control
Unfortunately, there is not a way to do this with stock Android.  There may be OEM (Samsung, LG, etc) features that allow this but I'm unsure if they exist.

There is an app that allows you to lock Media Volume, though.  It's called Rocker Locker:
https://play.google.com/store/apps/details?id=com.tomwandroid.rockerlocker&amp;hl=en

[Edit]  The above app reports significant battery drain.  This app may be a better alternative, NGC 4388:
https://play.google.com/store/apps/details?id=catchpower.gogo.blackholeaddons

Of course, there's always the option of writing your own volume panel changes then compiling your own OS binary from source.  :)