Hi Nartana,
Sorry for the late reply.
General gearing and gemming was directed toward full stam. Full stam gems in all gear, regardless of socket bonus and stam trinkets as much as was available at the time. CTC cap is not a concern for this fight.
( * Since then I've adjusted some gems to benefit from specific socket bonuses based on rate of return between stamina and mastery that was calculated recently by Theck, as seen here:
http://maintankadin.failsafedesign.com/forum/viewtopic.php?f=3&t=32711 )
In terms of CDs used for Impales, they were developed based on the order we tanked the Mutated Corruptions, including the premise that we killed every Corruption within 2 Impales with the exception (during progression) of the last Corruption which we sometimes got a 3rd.
I can't speak exactly for the CDs Rigg used on his DK, but these are generally what I use.
PLATFORM 1, IMPALE 1: Divine Protection + Enter the Dream (Ysera's toggle)
PLATFORM 2, IMPALE 2: Guardian + Ardent Defender + Divine Protection
PLATFORM 3, IMPALE 1: Divine Protection + Hand of Sacrifice & Divine Shield (external: holy paladin) + Pain Suppression (external: disc priest)
PLATFORM 4, IMPALE 2: Guardian + Ardent Defender + Divine Protection + Hand of Sacrifice & Divine Shield (external: holy paladin)
Hope that helps!