The flavor will mostly be in the oils stuck on the grinder burrs. The coffee making group should be fine, but could be a minor contributor. In regular grinders and machines, you'd grind through some rice or Grindz, and that would do it. The group could be washed with a regular espresso machine cleaner. You need to call a De Longhi rep to find out how the equivalent can be done in an all in one super autos.
While it is likely that some of the flavor is coming from the grinder, some of the operating mechanisms I have seen from super-auto machines have a lot of plastic parts in the mechanism that come in contact with the coffee.
I do agree that Grindz may be a way to get the flavors out of the grinder, but also that you should contact not only Delonghi but also Urnex to see what they say about using Grindz in a super auto.
You might also try getting a pound or two of some economical beans and keep making drinks until the artificial flavor is gone.
You should be able to find Durgol at Sur La Table in Portland.
I imagine that between the Durgol, and putting some grindz tablets through the grinder, your coffee should start tasting normal after a seasoning shot or two.
Woah, wait on the Grindz. I swear I remember hearing never to run grindz through Super Autos. Something to do with the careful calibration and the lack of being able to adjust it easily. I would double check this though as it is late now and I am tired.
*Oh, you're also never supposed to run flavored or oily beans through them if I remember correctly.