I was running an Unholy tank with my group to start, and all I needed to do to ensure I never lost aggro (even when chain lightning was macroed in as about cast #5 in my shammy rotation) was not to start dps until pestilence had hit. The first six casts of your multi-target macro I didn't actually have macroed, because beyond pestilence it was a blood boil/death strike mix with glyphed pestilence to never have to manually reapply diseases,

The other reason I didn't macro the inital casts is, because they are spell casts and I didn't have the 17% additional hit, every now and then they would miss and need to either be reattempted manually, or I would lose a hell of a lot of aggro from the missing damage. (As unholy most of the secondary rotation is uneccesary as long as you have your diseases ticking over and are using rune strike whenever available)

I have also been tanking as Frost, and the problem I see with your multitarget macro is that you are thinking like most DKs in that you must have both your diseases up on all mobs at all times (like Unholy). Once I did some reading, I glyphed howling blast to apply frost fever and went to a single disease rotation and it works fantastically well as you never need manually apply any diseases or even refresh them; Howling Blast does a ton of aggro and takes care of the disease refresh.

DnD --> Howling Blast --> Blood Boil --> Obliterate --> Blood Boil/Blood Strike x 2 --> repeat from howling blast

For single target and boss rotation I went back to the standard 2 x disease + Obliterate routine.