A decoding method for decoding two audio signals, comprising the steps of: receiving a first signal and a second signal corresponding to a time frame of the two audio signals, wherein the first signal comprises a first waveform-coded signal comprising spectral data corresponding to frequencies up to a first cross-over frequency (k y) and a downmix signal comprising waveform-coded spectral data corresponding to frequencies between the first cross-over frequency (k y) and a second cross-over frequency (k x), wherein the downmix signal corresponds to a sum-signal in a sum-and-difference representation, and wherein the second signal comprises a second waveform-coded signal comprising spectral data corresponding to frequencies up to the first cross-over frequency (k y), wherein the first and the second waveform-coded signal as received are waveform-coded in a left-right form, a sum-and-difference form and/or a downmix-complementary form wherein the complementary signal depends on a weighting parameter a which is received in addition to the received first and second signals; checking whether the first and the second waveform-coded signals are in a sum-and-difference form for all frequencies up to the first cross-over frequency, and if not, transforming the first and the second waveform-coded signals into a sum-and-difference form such that the first signal is a combination of a waveform-coded sum-signal comprising spectral data corresponding to frequencies up to the first cross-over frequency and said downmix signal comprising spectral data corresponding to frequencies between the first cross-over frequency and the second cross-over frequency, and the second signal comprises a waveform-coded difference-signal comprising spectral data corresponding to frequencies up to the first cross-over frequency; receiving high frequency reconstruction parameters; extending said downmix signal to a frequency range above the second cross-over frequency by performing high frequency reconstruction using the high frequency reconstruction parameters, receiving upmix parameters, mixing the first and the second signal so as to generate a left and a right channel of a stereo signal (412a-b), wherein for frequencies below the first cross-over frequency the mixing comprises performing an inverse sum-and-difference transformation of the first and the second signal, and for frequencies above the first cross-over frequency the mixing comprises performing parametric upmixing of said downmix signal by using the upmix parameters. receiving a first signal and a second signal corresponding to a time frame of the two audio signals, wherein the first signal comprises a first waveform-coded signal comprising spectral data corresponding to frequencies up to a first cross-over frequency (k y) and a downmix signal comprising waveform-coded spectral data corresponding to frequencies between the first cross-over frequency (k y) and a second cross-over frequency (k x), wherein the downmix signal corresponds to a sum-signal in a sum-and-difference representation, and wherein the second signal comprises a second waveform-coded signal comprising spectral data corresponding to frequencies up to the first cross-over frequency (k y), wherein the first and the second waveform-coded signal as received are waveform-coded in a left-right form, a sum-and-difference form and/or a downmix-complementary form wherein the complementary signal depends on a weighting parameter a which is received in addition to the received first and second signals; checking whether the first and the second waveform-coded signals are in a sum-and-difference form for all frequencies up to the first cross-over frequency, and if not, transforming the first and the second waveform-coded signals into a sum-and-difference form such that the first signal is a combination of a waveform-coded sum-signal comprising spectral data corresponding to frequencies up to the first cross-over frequency and said downmix signal comprising spectral data corresponding to frequencies between the first cross-over frequency and the second cross-over frequency, and the second signal comprises a waveform-coded difference-signal comprising spectral data corresponding to frequencies up to the first cross-over frequency; receiving high frequency reconstruction parameters; extending said downmix signal to a frequency range above the second cross-over frequency by performing high frequency reconstruction using the high frequency reconstruction parameters, receiving upmix parameters, mixing the first and the second signal so as to generate a left and a right channel of a stereo signal (412a-b), wherein for frequencies below the first cross-over frequency the mixing comprises performing an inverse sum-and-difference transformation of the first and the second signal, and for frequencies above the first cross-over frequency the mixing comprises performing parametric upmixing of said downmix signal by using the upmix parameters.