Which "Input terminal configuration" should I use for USB-6216 and PCI-6221?

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I am confused about the "differential" and "single-ended" options on my DAQ devices, and would some help!

Currently, I have two DAQ devices (USB-6216-BNC and PCI-6221). According to the device manuals, both devices have 8 differential (or 16 single-ended) AI channels.

For USB-6216-BNC, it looks like this. As you can see, there are 8 BNC channels. So, I have always assumed that they are "differential" channels.

  (Figure 1)

For PCI-6221, it is connected to a BNC-2090A, and it looks like this. As you can see, it has 16 BNC channels. So, I have always assumed that they are "single-ended" channels.

 (Figure 2)

I use LabVIEW (2009 SP1) and DAQmx 9.3 on computers running Windows 7 (64-bit) to control my DAQ devices. I usually record EEG signals, via a BNC cable, and then into the first AI channel (AI0). When calling the "DAQmx Create Channel (AI-Voltage-Basic).vi", there is an "input terminal configuration" parameter that needs to be specified. For this parameter, there are a few options (default, RSE, NRSE, Differential, and Pseudodifferential). For clarity, here are two screen shots. 

 (Figure 3A)     (Figure 3B)

Here are the questions that I need help:

1. Should I use "differential" (instead of "RSE" or "NRSE") when using US-6216?
2. Should I use "RSE" or "NRSE" (instead of "differential") when using PCI-6221 via BNC-2090A?
3. When using PCI-6221 via BNC-2090A, should I flip the switch (marked in green on Figure 2) from "DIFF" to "SE"?
4. On BNC-2090A for PCI-6221, there is a switch (marked in blue on Figure 2) determining whether a channel is "RSE" or "NRSE".  Is this switch for all the AI channels? OR is it just for the AO0 and AO1 channels?

Any comments will be appreciated!!!