Basically the big caveat is that the DR2X if placed in the external controller mode, the transmitter looses internal PL injection and an external PL is required. I developed a $5 Arduino nano that would create any one of the standard PL tones and inject it into the DB 15 pin connector.. .
Which is another problem.
The DR2X external controller looks like a VGA 3 row DB15 connector except you can't use a VGA cable as not all 15 pins are available or used. First I ordered just the connectors and figured I'd save money making my own connector, the DB15 literally melted as I soldered pins. What crap we got picking up connectors at a swap-n-shop from some vendor.
I remember I had to order a high density (3 row) DB-15 1 to 1 patch cable from one of the electronic suppliers like Digikey or Mouser.It was about $15 plus $8.95 shipping. Then cut it in half, and ring out the colors to the pins. The cable I did buy had a "frame ground"- bare wire, which I felt was a quality touch.