Interesting that you find the D2 blade easier to sharpen than M2. I have always thought that M2 was very easy to sharpen to a shaving sharp edge. In fact I find it easier to get my BM140 Nimravus shaving sharp than to do the same with any of my BM 154CM knives. Now, admittedly, this is annecdotal so refutations are welcomed!
As for D2, I have the 806D2 but don't carry it often due to size -- don't like the reaction I get when I pull it out in public so I stick to small knives around town (705, mini griptillian, and now the BM960). So it follows that I don't have much need to sharpen it. Of course the BM960 also sports a D2 blade so I should soon have reason to experience sharpening D2.
BTW, any comments on sharpening S30V and general comments on N690?