I'll try to explain it as I hear it. The stock sounds a little steril to me, especially on say kick drums and low bass notes. The warm mod adds a little bit of roundness to the bottom end, the notes seem to have more depth and sustain. Then of course you get the oade sig. high end, very smooth and detailed on good systems. Realize that the modded units also require better playback gear to truly take advantage. I've heard the warm mod described as "muddy" by people who listen on car stereos and consumer grade playback gear, which is nonesense but I can see how they come to that conclusion. I think all of Doug's mods offer a warmer sound from the stock, but the different flavors offer different emphasis with the coloration or lack there of with the Tmod.
Hope that helps a bit...