The DUAL MIXER 27b is composed of two 3X1 mixer sections.

Mixer 1 is normalled to Mixer 2 for default 6x1 operation. Inserting a plug to Mix Out 1 breaks the connection and then provides 2 seperate 3x1 mixers.
Mixer 1 is good for Voltage mixing and processing with inverting/non-inverting attenuators and Offset Control
Mixer 2 is ideal for audio mixing as attenuators allow easy full attenuation of signal. Both sections will work well for both audio and CV mixing.