I'm using a Debian and I have very frequency rich headphones. That has the good effect that I can listen to my music in incredible quality, but has the downside that if anyone messed up their soundmix (as happens often to me on YouTube) I'll get all kinds of high frequency noise.
So, I'd like to be able to change the relative output of frequencies through a plugin or through a program for my linux.
Bonus if the program has predefined templates for headphones / techno / classical / etc.
Another use is that I have music play software that doesn't have a mixer build in. Now when I listen to my favorite radio station I want to adapt for the relevant genre I'm listening to.
CLI or GUI is both fine to me. I'm willing to pay up to 20 € for such software. Open Source is a plus, but not required.