But when it come to 6.1 and 7.1 soundtracks the rear surround channels and front presence surround share the same internal amplifiers. This means that the rear surrounds and the front presence channels are mutually exclusive and they cannot play simultaneously. The receiver decides which pair to enable and which pair to disable based on the source material. For 5.1 and fewer channel sources, the front presence channels are enabled and the rear surrounds are disabled. For 6.1 and 7.1 channel sources, the front channels are disabled and the rear surrounds are enabled. This means that for 6.1 and 7.1 soundtracks, the front ambiance gets mixed in with the main speakers and the results can sound muddy. You also lose the dialog lift effect.