1. Multi-channel audio decoder for processing a parametric representation, wherein the parametric representation comprises information on one or more spatial parameters describing spatial properties of a multi-channel signal, a stereo parameter describing spatial properties of a stereo downmix of the multi-channel signal, and a monophonic downmix signal, the decoder comprising: a bitstream decomposer to decompose a bitstream into the stereo parameter, the information on the one or more spatial parameters, and a monophonic downmix signal, the monophonic downmix signal being a monophonic downmix of the multi-channel signal, comprising a hardware implementation thereof; a parameter reconstructor for combining the stereo parameter and the information on the one or more spatial parameters using a combination rule to obtain the one or more spatial parameters; wherein the stereo parameter and the information on the one or more spatial parameters, when combined using the combination rule, results in one or more spatial parameters, comprising a hardware implementation thereof; a upmixer for deriving a reconstruction of the multi-channel signal using the monophonic downmix signal and the one or more spatial parameters obtained by the parameter reconstructor, comprising a hardware implementation thereof.