Download of SpeakerAmp 6.0 for Mac was on the developer's website when we last checked. We cannot confirm if there is a free download of this app available. This free Mac app is an intellectual property of Nimblesnail. We recommend checking the downloaded files with any free antivirus.
From the developer:
SpeakerAmp lets you amplify, equalize, and boost your audio with 3-D surround. It increases system-wide volume up to 9x louder beyond the max Mac normal level.
The tool works with any output device. You can set the volume range for each device individually. For instance, you can set lower values for headphones and higher levels for a soundbar. The app changes the settings automatically upon output device selection.