send us a pick of the overspray. even though it's their responsibility to get your printer running, being able to discuss your issues in the right terminologies and have some basic understanding of what may be occurring will give you a better chance of them taking your seriously.
if you were to run a test pattern so that we could diagnose. one thing to do is create an image (2 x 8) of c, m, y, and k. so you can isolate if it's one color or all colors. if it's coming from one color, do a damper swap to see if you might have a bad cartridge/ink that is causing. ...see if the overspray jumps to a new channel during the damper swap.
then do a grayscale image with 100%, 90%, and so on. run this test print with grayscale selected so that just the black portion of your heads operates. this will isolate the fine and very dithering abilities of the head. some heads will be fine blasting ink, but not at faintly misting ink. also compare test prints in bidirectional and unidirectional. (make sure that your rip is set to variable dot)
also since it's a dual dx5, see if you can tell if the overspray is coming from different passes thus coming from one head or is it unilaterally all the nozzles, all the nozzles from one color, and adjust head height.