Was bug #50 in bugzilla
Audiomanager telco 7.5.2013:

Lorenz proposed to have a mixer as grouping element similar to crossfader, gateway etc. It should have 1 ... x inputs and 1 output.

Volumes for mixing should be tweaked like today with the properties of the single elements like sinks. sinks and sources of the mixer shall be registered in addition to the mixer.

proposed by @JensLorenz