It’s been a long time since I used R-Box. If one would suit your purposes, the appls VLC and SM Player both take playlists and have built-in, easy-to-use EQ. (My needs are EQ are modest right-now.) See VLC’s ‘tools’ menu or SMPlayer’s ‘Audio/Equalizer’ (once something’s playing).

If you were to switch to using Pipewire for audio, the EasyEffects program has EQ in it’s big-bag-o-tricks.