For anyone who's interested: this is my polished version of the code.
(Sets up T4 in SPI Slave Mode and receives 16Bit Values with DMA)
#include <DMAChannel.h>
#include <SPI.h>
#define PRREG(x) Serial.print(#x" 0x"); Serial.println(x, BIN) //Serial.println(x,BIN)
#define SAMPLES 1
#define...