I recall iffy signals, in one of his recent videos, saying something to the effect that the XTE uses the same processor as the 700 and the XTE is basically a 700 without a few of the more advanced settings. Considering the Expedition Pack comes with 2 coils and the wireless phones, that's a pretty good deal for the money especially if you're one who probably won't be messing around with advanced settings.
I just picked up an X-Terra Elite Expedition pack. I haven't seen Iffy Signals video, but I'll have to look for it because I totally agree with him and did a post on the Friendly Metal Detector Forum about the same thing.
I have a hunch/theory about the NOX's and X-Terra's, can't prove it yet, but I'm in the process of trying to either get confirmation, or to find out if I'm wrong. Although I could have bought any of the NOX's, I went with the X-Terra Elite because I think they're all the same detector (NOX 900, NOX 700, X-Terra Elite, X-Terra Pro). The difference in the detectors would simply be how the software/firmware for each detector was programmed. Certain features could be limited on lower cost models, higher cost models get more features.
That would explain why you can swap coils between any of these detectors, but not the Manticore, as the Manticore is a totally different detector, with different electronics and internals. It would also make business sense for Minelab to make only 1 detector that they can turn into 4 different models. That would save them huge $ on inventory costs, components needed to build, etc. Again, at this point, it's just a hunch/theory I have, but I think I'm right and I'm reaching out to see if I can get confirmation, or if I'm totally off track.