Certain instruments from BFD Percussion don't come out the channel they are assigned to. Shiko Toms, Djembe Toms, Tambourine, and some others come out the Snare channel.
For example, assign the Djembe Toms Tom Floor to the Floor Tom channel and it comes out Snare channel. Setting the output assign doesn't affect anything. The instruments that behave like this can't be mixed. They're all on the same channel with one volume and one pan.