Ok. I think I got it but was confused becase I forgot that JRiver treats the 5.1 mapping as FL, FR, C, SW, SL, SR, but after adding 2 extra channels the mapping changes to 7.1 container FL,FR,SW,E1,E2,SL,SR. Does it make sense to maintain standard 5.1 mapping and add the extra channels after the SL & SR?
One other question about the order channels config option. That only handles up to 7.1 channels, so could the extra channels be added to the list of available channels to reorder?