A DIY tune is the same thing Mark Lawton does for you. Adds Fatmat or Dynamat to the cups, drivers and various parts of the drivers (front and back), and with his angle pads it is, as jibzilla said, considered a level 1 full tune. This is what I experienced with my D7000. It literally went from a good headphone to a great one, which is why I'm taking a leap of faith that the TH900, which is already an amazing headphone, will be just that much better. At this point I'm doing just the tune without the pads but I have a pair of spare angle pads at home I can put on for testing once I get the TH900 back.
There are many YouTube videos about the Lawton mods - just search for it and watch a bit of it. Very simple mod, easy to do yourself but best part is it works.
I posted about doing this mod once before as a question and got nothing but "why are you messing with a great headphone", and many other comments along that vein. With that, I also got a couple of PM's from guys who did the tune but didn't want to ignite a firestorm, and they both thought the improvement was clearly there, and worth doing. It's $99 to have Mark do it. That is not a huge investment, and I'm at the point of fine tuning my favorite headphones right now. Just sent my D7000 to BTG audio to have a Q French Silk cable swapped in for the stock item, so that headphone will be DONE.
I realize some guys think I'm crazy, but so what? It's my headphone and if they come back improved, which I have no doubt they will if my experience with the D7000 is an example, I'll just have a better than stock TH900, which also has a Q French Silk cable that was put on by BTG when Greed owned this pair.