This problem is with input slot, not output. Single recipe requires 10 redstone. So 16 centrifuges needs 160. But only one stack are available, so only 6 of them works.
Hm, that should be fairly simple to fix, it just needs to look for a second stack of the same type, which is probably a good idea even if no one likes my solution. I'll see about figuring out how to do that later.