I will confirm the observation that IL2 recognizes only a maximum of 4 USB controllers. It's a hard limit that you can't change.
Here's the even more fun thing about that: say you have 6 controllers attached (which is not that hard to do, depending on your flight sim gear). IL2 chooses which
of them it
decides to see. IL2 places them in some order based upon its own algorithm, and only acknowledges the existence of the first 4. And you can't change the order.
(Il2 does not necessarily place them in the same order you see them in the Windows 'Game Controllers' window.)
It would be GREAT if the guys who make the mod packages would fix this. I can't imagine that it's hugely difficult compared to modding flight models, etc.
In any case, I had been using a CH Products
Throttle Quadrant unit for levers and switches in IL2. I had to disconnect and retire it when I got the X55 in order for IL2 to see both the stick and the throttle.
In a perfect world, IL2 would be like DCS World, which sees and reports every control device you have connected, no matter how many.