M-DAX is a kind of sound processing that can boost the bass and treble of lower-quality MP3 files or other audio of dubious heritage. M-DAX is probably best ignored most of the time and the Direct Mode cuts out the sonic influence of M-DAX and the tone controls.

What does M DAX do?

The “M-DAX” function generates the signals eliminated upon compression, restoring the sound to conditions near those of the original sound before compression. It also restores the original bass characteristics for a rich and expanded tonal range.

Is Marantz still good?

It's one of the truly great brands in audio that have somehow managed to survive in the market. Marantz has a reputation for innovation, manufacturing consistently and producing high quality and reliable products even though the brand has had 4 different owners since Saul Marantz started the company in 1953.