I've been playing my DRK at level 80 for about a week now and I've never had any major issues with MP management, if I eat a buster raw its not because I didn't have the MP to use TBN, its because I didn't clip the snapshot, I.E: I was simply too slow.

Syphon Strike, Blood Weapon and Delirium are more than sufficient to upkeep your MP at acceptable levels, unless of course you're spamming Edge of Shadow like a madman (which you shouldn't be, unless you're STR potting a burst window there's no reason you to weave Edge or Flood more than once every thirty seconds.)