My first attempt was to just set layout to AE_CH_LAYOUT_7_1, but that would replace FLC with SL. In case of out of spec AAC files, we get FL,FR == SL,SR and FLOC,FROC are in  FL,FR

See the following sample: https://dl.dropboxusercontent.com/u/55728161/Channel-Check-Lots-of-Formats.mkv

Besides that, I am still not happy.