Thanks for your reply.
So I dismounted the sensor and gave it a closer look… in fact the wires on the "D" and "E" Pin are connected like you said.
Just to clarify, there aren't any other components it's just the 4 pins of the sensor hooked up to wires going directly into the Felix Controller board.
D + E -> black wire.
"+" on side together with "E" -> red wire (I'm thinking this should be the IR LED)
"+" on side together with "D" -> yellow wire (guessing that's the receiver)
So for X min as an example what I'll do is connect it as follows:
black wire -> GND (blue, middle pin, in the Smoothieboard pinout schematic)
red wire -> 5V (orange)
yellow wire -> x min (P1.24) (green)
I got cautious when i read the warning in the "printer guide" about potentially frying the board and in the search that followed I found a lot of schematics with similar sensors on reprap forum which have some resistors and voltage regulator on a small pcb. I thought it was best to double check if it's OK to hook it up directly.
Thanks four your help!