ReadyNAS 102 doesn't display anything over serial, but won't boot when serial is connected

Hey guys, I'm really at my wits end on this. I'm trying to connect to my ReadyNAS 102 over serial so I can eventually install a newer distribution of Linux, but I'm not getting any data from the serial port. The weird thing is that the system refuses to boot when the serial port is connected properly, so it must at least somehow recognize when it's properly connected. 

I'm connecting with with a baud rate of 115200, and am hooking up the pins as shown here. (I have also experimented with moving the pins around, and the system then boots just fine but of course still displays nothing on the serial link)

I've pretty much hit a brick wall at this point, so any help you can provide will be much appreciated!