[AE/CA] - on LPCM only set audio-midi-setup to 8 channels when needed based on the channelcount of the stream with the highest channelcount - else set it to 2 channels if stream is only 2.0. This allows amps to switch to stereo enhancing modes (e.x. DPII) when playing 2.0 over LPCM (e.x. AAC 2.0).