I guess there are a lot of ways you could go but I offer this idea. You leave the plugins volumes and routes as they are and create a new audio output port for the Media Players.
and in the songs you change the Media Players to that port. Now there is a Media Player port volume slider in the Monitor window where you can globally adjust the Media Player volume for all the songs that are routed that way.
The port still routes through the Song Gain or Master Gain so it acts as a sub port.
You could do the same with the Plugins to have their own port if you wanted to.
Anyway that’s my idea, I hope it helps .