Issue connecting breakout board to Arduino with UART?

I'm using a DigiX (Arduino Due based) board to connect to a GPRS/GSM SIM908 breakout board. The board has the following pins on its RS232RS232 pinout

. I've got all three UART TX lines hooked up to the RX Lines (and RX to TX) on my arduino but the board keeps resetting, which I would guess is some sort of voltage issue (I turned the board off immediately). However there are three MAX3232s on the underside of the board, which I thought would have made it so I could just connect the lines directly to the arduino. Any idea why this is happening or how to properly connect these two devices? Any help is much appreciated, thank you