You can use as many as you want, all are supported. Only IL-2 doesn't support more than 4 in it's own controller setups.
If you need it, I can send you identifiers for ID 5, 6, 7 etc. But you can probably manage most assignments by just typing in the number 5 in the "5joyx" "5joyy" "5joyz" in the config files for ID 5, and trying X Y Z, as those are the most common axis letters for devices. Should find most pretty quickly in this way. The joystick ID programs are just to help people identify their stuff without trial and error. With trial and error you can find anything.
Neat way of getting around IL2's limitations eh?
In fact, one can manipulate most functions, trims etc using device link. I have not put in that support though but I could if it would be useful to people. Most people do not have more than 4 devices (even though I do, I used to have my G940 main steering wheel as elevator trim, mounted properly on my left side like in Bf 109. But it was a bit bulky and my chair kept bumping into it, and not enough USB ports etc. I now use the back R2 wheel on the throttle of the G940 as trim instead, which is okay. A but unrealistically fast perhaps).