Here is the back of an EX4:

And here is the back of a DX3:

(Sorry about the scale, but that is all Lowther offers.)

Note that under the EXx cover is the complete, unmodified DXx frame, basket, whatever, including the binding posts.

As to T/S changes, I doubt that there is any change at the small signal level, but major changes at large signal. I have not measured these. The EXx cover severely damps the back wave. An EXx will not load a resonant cabinet, whereas a DXx works just fine in a MLTL.

If you buy a new EXx, you get the lemon squeezer phase plug. New Dxx comes with the bullet phase plug. I prefer the bullet, but YMMV. I would have brought my MLTL's loaded with DX3's to LSAF, but....

Bob