One relevant point I can make, because I had discussed EDS detection limits previously with Keith Thompson before he left Thermo, is that if one is using the Bruker EDS interface, with Probe for EPMA for integrated WDS and EDS point quantification, Bruker does return the background intensities (needed for calculating detection limits), along with the net intensities from the EDS spectrum. However Thermo does not.
My recollection, from what Keith told me, is that Bruker can easily return the background intensities along with the net intensities because they construct a full model of the continuum. At that point, it's simply a subtraction problem. Therefore, based on whatever the current ROI is for the element in question, Bruker can return the net intensities and also the background intensity. However, because Thermo is using a "filter fit" method for obtaining the net intensities, calculating the background intensities is more difficult.
That is about as much as I know so I'm going to wait for some experts to weigh in on this question.