I found this via Google and noticed it has never gotten answered, so I did some more research. There are a handful of files not consistent across BGEE, BG2EE and IWDEE. They are:
XXXXXXXw.wav : Reaction to Party Member Death (BG/IWD)
XXXXXXXx.wav : Annoyed Acknowledgement 1 (BG2/IWD)XXXXXXXy.wav : Annoyed Acknowledgement 2 (BG2/IWD)XXXXXXXz.wav : Critical Hit (BG2)XXXXXXX_.wav : Action Acknowledgement 4 (BG2/IWD)XXXXXXX#.wav : Annoyed Acknowledgement 3 (IWD)
For example, to create a BG2 sound set from an IWD one, you'd need to come up with a Z sound (e.g. just copy and rename the battlecry sound). The annoyed acknowledgements could always be created from the regular acknowledgements, and etc. All sounds need to be 22khz mono wav files.
Once you've gotten your sound set, you can install it with WeiDU, or the more simple way is to create a folder named sounds in the same location as you would custom portraits; i.e. with Steam for Mac it's
~/Documents/Baldur's Gate - Enhanced Edition/sounds~/Baldur's Gate II - Enhanced Edition/sounds
~/Icewind Dale - Enhanced Edition/sounds