Currently I am playing a Dirgesinger (bard kit of the Song and Silence mod). His main special feature is a song that will curse enemies, causing a malus of –1 to their THAC0 and saving throws. Which is neat for the beginning of BGII, but doesnt cut it later on in the game - let alone in ToB.
As his song doesnt improve like the Skald’s or Jester’s I would like to fix that with Shadowkeeper to make it all a bit more worth his while. At level 15 a malus of –2, and perhaps at level 20 a malus of –3.

However I dont know my way around with SK, having only used it for changes of proficiencies so far. And after looking into his statistics with SK I found nothing referring to his bard song (which doesn’t mean its not there ;) ).

Can anyone help me out here? Where to look, what to do?