CineMag/Reichenbach Engineering is one of the pioneers in making audio transformers specifically configured for direct box applications.  One of the assets setting a true direct box transformer from another style is the method the input signal is isolated from the signal on the output of the transformer, which is done with Faraday shields.  These shields consist of  conductive layers (typically copper foil) that are interposed between windings, which are electrically connected to the signal ground.  Unlike a microphone input transformer with only one (1) Faraday shield, direct box transformers have two of them.  This way, the signal ground of the source has its own Faraday shield, and the preamplifier receiving the signal has its totally separate Faraday shield.  This is important to avoid ground loops which will cause hum.

A direct box transformer takes a higher level signal usually from an instrument and reduces the signal to microphone level.  This accomplishes certain objectives.  The sent signal level is made to be compatible with the microphone preamplifier.  The other attribute of using a direct box transformer to do this is that the transformer makes the impedance on the secondary to be very low.  That allows for excellent bandwidth when driving the cable even if the impedance of the incoming signal is high.