ffmpeg -loglevel verbose -i Venice.mov -pix_fmt yuv420p -codec:v libx264 -x264opts rc-lookahead=46:keyint=46:min-keyint=92:no-open-gop=1 -level 4.1 -preset slow -filter:v hqdn3d=4.0:3.0:6.0:4.5 -map 0:v -crf 26 -maxrate 2M -vf scale=-2:540,setsar=1:1    -force_key_frames "expr:eq(mod(n,46),0)" -filter_complex "[0:a:6][0:a:7]amerge=inputs=2[aout-stereo]" -map "[aout-stereo]" -c:a:0 aac -ac:a:0 2 -ab:a:0 128k -filter_complex "[0:a:0][0:a:1][0:a:2][0:a:3][0:a:4][0:a:5]amerge=inputs=6[aout-surround]" -map "[aout-surround]" -c:a:1 ac3 -ac:a:1 6 -ar:a:1 48000 -ab:a:1 640k -dialnorm -24 -dsur_mode 0 -original 1 -dmix_mode 2    -y   Venice.tseng_1080p_2398.mov_1_libx264.ts

Using -channel_layout 63 in the AC3 encoder triggers a 5.1 layout for the AAC encoder as well...????