DeskFX comes with an easy-to-use interface that gives you the power to boost your audio. For $4.99 a month, you unlock advanced features like gapless playback, a built-in 10-band equalizer, unlimited cloud storage space with its Vox Music Cloud, a refined studio-like listening experience, playlist syncing and deeper customization options and a ton more. Although this app is free, there are some features locked in its premium version. It helps decrease or mute sound for your sound file too. Music equalizer boosts volume and ensures no distortion when increasing - Boost your music file volume with one tap. Import music from Files App & iTunes music library Key features - Helps various types like mkv, mp4, aac, avi, mp3, mov, aiff, m4a. Control the audio of each of your apps independently with per-app volume, EQ, balance, and audio routing. Sound Control is a unique application that adds advanced audio controls to your Mac. Download the Jabra Sound+ App to unlock the full potential of your headphones, including access to exclusive features available only through the app, and the latest firmware updates to help keep your headphones at the top of their game. (Boom and the AU/Soundflower trick don't apply here in my case, as neither seem to work with Airplay).Jabra Sound+ App. Point is, with these EQ plugins, the signal is audibly degraded even with no EQ applied, simply with the plugins active. All this to say that I hear every little change in the signal, and the quality of the signal using no eq plugin is pretty good. I am streaming Spotify using OS X Mountain Lion AIrplay (which sounds better than Airfoil, which I was using before, by the way) to an Apple TV, which I have connected via Toslink cable to a high quality DAC/ tube preamp, which feeds a good solid state power amp, which in turn powers very high quality (I hate the term 'audiophile') speakers that produce excellent frequency response from 30 Hz - 20 kHz. Here's my two cents, as I am interested in having quality EQ in my rig, and I thought, 'why not try digital first?' So, I just checked out out Hear, Boom, and DPS.

Imac equalizer app