  We study mixed unitary channels generated by finite subgroups of the group of
all unitary operators in a Hilbert space. Based on the majorization theory we
introduce techniques allowing to calculate different characteristics of output
states of channels. A class of channels has been allocated for which the use of
entangled states doesn't give any advantage under taking supremum and infimum
for output characteristics of channels. In particular, $l_p$-norms are
multiplicative and the minimal entropy is additive with respect to taking
tensor products of channels. As an important application of the obtained
results the classical capacity of channel is calculated in the evident form. We
compare our techniques with the informational characteristics of Boson quantum
channels.
