The price point is a major factor on these 2 almost identical interfaces but the thing to bare in mind especially for live performances is that there is no need for cabling from the desktop to the stage on the xr version as opposed to having wires and/or snake cables when running a front of house set up. for me that is worth the extra money, plus I do prefer the xlr aux outs on the xr as well.
I can hear the first track plus the the signal that will be the second track but as soon as I press record I lose the sound from track two but I'm still hearing track one ! This in my opinion is a flaw with the mixer design. I have the same exact problem and the only way around it is to disable the usb codec and use the soundcard that is in your computer, and basically you would just use the mixer as a preamp. The way to do this is to use the FX out on the channel you are recording into the mic in on your computer, and run the audio out from your computer to rca in on the mixer. You'll have to adjust the volume levels to get the mix your looking for. This pretty much makes the whole usb concept redundant, but if you want to hear what ever it is your recording along with a pre-recorded track in real time (i.e. live) this is the only way to do it. It seems pretty stupid that this mixer is set up this way, I'm wishing I would have bought the cheaper model without the usb because it would work the same way. "but", if you don't mind not being able to hear what your recording in real time, the usb function works quite well. You probably won't find a behringer mixer in this price range (new) that allows you to monitor what your recording in real time whilst playing back another track. "way to go behringer".