Acid malt is coated in lactic acid, but you can use any malt as a source for lactobacillus. The problem with using grain as a source for your bacteria is that you can't be sure exactly what you are going to get. I would guess that the DMS you are smelling isn't from the malt (per se) but from some strain of bacteria that was living on the grain.
I've had good luck using a culture of Lactobacillus from yeast labs. I also bring the wort to just below a boil to ensure that none of the "other" microbes from the mash/grain make their way into the fermenter. I've never had an issue with DME, but a healthy ale fermentation goes a long way to driving it off.
If the aroma gets worse, you should consider waiting until you like the sourness that has been produced, then boiling the wort for ~30 minutes before cooling and pitching the yeast as normal. The boil will drive off the DME produced by the bacteria, so you can have your sourness and drink it too.
Hope that helps, good luck.