Actually forgot to mention with the 8bitdo and Xeox gamepads that you need to use direct input and not X-input for these to work, the same as you would on AmigaOS 4. Both pads make use of lowlevel.library and sensors.library.

Poseidon seems to identify this automatically as hid.class so am not really sure this should be an issue but is handy to know in case you need to manually attached it. I have found with my Xbox One Controller that it didn't recognise the Xbox360.class straight away and had to attach so i guess identifying the hid.class of a pad may help if Poseideon doesn't automatically pick this up.