I think that a mixer or more in general having the ability to control the audio of each tab just by right clicking on the tab on the explorer would be good.
Let's say i have tab A,B and we want to put the tab A at 50% volume and tab B to 100%, i think that would be a good feature.
It would be even better if we can boost the audio of each tab over 100%, like at 120% or 200% without installing extensions.