No you do not need to change the number of channels, AC3/DTS is compressed and fit within the bandwidth required for uncompressed PCM 2.0.
See http://kodi.wiki/view/Audio_troubleshooting#Why_5.1_is_possible_when_number_of_channels_is_2.0.3F and http://kodi.wiki/view/audio_quickstart_guide for more information