No one has made a definitive statement on what "breaking in" a DMT does. There has been some speculation but nothing definitive. maybe it fractures some of the diamonds that are sticking up above the rest? Maybe it simply dislodges some of the diamonds that are sticking up further from the nickel layer they're embedded in?
I think the DMTs are going to sound different from everything else mainly since the base is a slab of metal. I didn't really try to break in my DMT8C other than to run a screw driver shaft at an angle on the edges. I figure the 325 and even the 1200 are so coarse (it's going to matter more on the later grits) that it's not really going to make a lot of difference.
I'm not sure if I damaged my 1200 (before I got the 325) by lapping my shaptons. I don't think so. It now appears (and pretty much feels) to be almost perfectly smooth. Like you used a blowtorch to melt the layer of nickel on it. But it still cuts and leaves the expected scratch pattern. Oddly enough, to the fingers, it feels way smoother than my shapton 2K and maybe even the 4K.