  Zero-error single-channel source coding has been studied extensively over the
past decades. Its natural multi-channel generalization is however not well
investigated. While the special case with multiple symmetric-alphabet channels
was studied a decade ago, codes in such setting have no advantage over
single-channel codes in data compression, making them worthless in most
applications. With essentially no development since the last decade, in this
paper, we break the stalemate by showing that it is possible to beat
single-channel source codes in terms of compression assuming
asymmetric-alphabet channels. We present the multi-channel analog of several
classical results in single-channel source coding, such as that a multi-channel
Huffman code is an optimal tree-decodable code. We also show some evidences
that finding an efficient construction of multi-channel Huffman codes may be
hard. Nevertheless, we propose a suboptimal code construction whose redundancy
is guaranteed to be no larger than that of an optimal single-channel source
code.
