Where do you see pins labeled + and -? If you right click on the device in MAX and select 'Device Pinouts', you will see that the pins are labeled ai0 through ai15. That's a total of 16 SE inputs. Each SE input requires you to reference the ai channel to gnd and a diff input requires you to use a pair of ai inputs. To use ai0 as diff, it must be paired with ai8 when wired. You do not specify the second channel in your phsical address control/MAX. So, your channel list might be dev1/ai0:8 with channels 0 through 6 wired for SE (referenced to gnd) and ai7 and ai15 being one diff pair and ai8 and ai16 being the second diff pair.
