A 040 additional info

In addition to the Dungeonscape Penetrating Strike alternative class feature, note there is also a Lightbringer Penetrating Strike ACF in Expedition to Castle Ravenloft (page 208). While the Dungeonscape ACF just says you get damage against a sneak-immune foe without qualifying that damage, the EtCR ACF gives you sneak attack damage with the normal dice, and thus will qualify for the benefit of Complete Adventurer's Staggering Strike feat. As these are ACFs with two different names you can choose either one.