After a lot of investigation, I didn´t found a working key configuration, online.
Also I could not access /dev/input/ to use jstest... Whatever, testing, testing, testing made the deal:
Working xBox360 wired USB Controller:

[Microsoft X-Box 360 pad] plugged = True plugin = 2 mouse = False AnalogDeadzone = 4096,4096 AnalogPeak = 32768,32768 Mempak switch = Rumblepak switch = Start = button(9) DPad U = hat(0 Up) DPad D = hat(0 Down) DPad L = hat(0 Left) DPad R = hat(0 Right) Z Trig = button(6) C Button U = axis(3-) C Button D = axis(3+) C Button L = axis(2-) C Button R = axis(2+) R Trig = button(7) L Trig = button(8) A Button = button(0) B Button = button(1) X Axis = axis(0-,0+) Y Axis = axis(1-,1+)

And to complete it, the iNext USB N64 Controller:

[Generic USB Joystick ] plugged = True plugin = 2 mouse = False AnalogDeadzone = 4096,4096 AnalogPeak = 32768,32768 Mempak switch = Rumblepak switch = C Button D = button(2) C Button L = button(3) L Trig = button(4) Start = button(9) Y Axis = axis(1-,1+) DPad U = hat(0 Up) A Button = button(6) DPad D = hat(0 Down) X Axis = axis(0-,0+) R Trig = button(5) DPad R = hat(0 Right) B Button = button(8) DPad L = hat(0 Left) Z Trig = button(7) C Button U = button(0) C Button R = button(1)

Seems all fine now, except connecting 2 N64, 1 xBox360 USB and 1 xBox Wireless-Adapter. ES displays, that no Controller is connected. They probably suck to much energy or it is related to the NesPi-Case I´m using :(

But that is another Topic :)