iPad to control Mac Pro computer audio system Technology
Mine

MacPro macOS
11.0.1 Big Sur

My wife's

iPad Pro
iPadOS 14.2

Stereo system
MacPro has a hardwired digital connection to my stereo system's DAC.
No other available inputs (wireless or bluetooth) into the stereo system.
So, I can not send music directly from any other device to the stereo system.  The stereo has no other inputs remote or otherwise.
I use Apple's Music app.
Works perfectly.
Goal
Enable my wife's iPadPro to remotely access my Mac Pro's Music app.
So she can play music on the attached stereo system.
Note: She has a different AppleID than I do, but I could let her use mine if it would help.
Thoughts appreciated.
This is kind of half an answer as it's been so long since I actually did this that the method is a bit hazy…
Apple's iTunes Remote - https://apps.apple.com/gb/app/itunes-remote/id284417350 There's a one-off sign in procedure to authorise 'foreign' remotes.