The MC624 is similar to the monitor section of a mixing desk: it lets you select one out of six stereo audio sources, adjust the level and route it to one of four monitor outputs.

The DI503J is a triple mode Direct Box for instrument and a Re-Amp unit for the '500' format of API*.

The PAD500 is a dual balanced line attenuator. It is used after a mic preamp or any effect that you want to drive hot without clipping your converters.

The REM624 is a remote control unit for the MC624 Monitor Controler.

It offers the same contols as the central unit (except headphones volume).