A schematic showing the DSP TU interface to the Icom IC-7100 is shown below.
The DATA 2 connector on the IC-7100 is used. The recommended audio input level on Data In (pin 1) is 100 mV. Since the open circuit AFSK output of the DSP TU is about 900 mV RMS, the signal needs to be attenuated. R1 and R2 reduce the AFSK signal to 82 mV. The resistors can be placed on the back of the DSP TU, then a Teykst ysct39a mini DIN 6 cable connects to the IC-7100. Check the pin out of the cable you get, as the colors seem to vary.
Since the DSP TU has transformer isolated AFSK input and output, and a floating PTT, while the IC-7100 has unbalanced inputs and outputs, several DSP connections are connected to ground.