Thanks for your effort, skellytz.
But maybe it's not the solution. Just finished my new installation dropping IA from my mod list completely. System language is German (before installation of vanilla BG manually switched to English to have game and mods in the same language, but switched back afterward), while installing mods. According to your post the characters needed should be included, so no problem. Installed everything with WeiDu v249, then used v246 for GB. No error messages whatsoever during installation. Starting the modded game before biffing is lagging but working (as before). After GB game crashes from starting screen with the known Chsound.cpp assertion failure. So nothing changed!?
That rules out IA as the culprit (not installed at all), but on the other hand my last stable installation was with GB (also without IA).
Azaghal