Maybe this is a pointless necropost, but felt like sharing after figuring it out a fix for the missing car crashing sounds.
To get both crashing and new weapon sounds, it seems the modified RESIDENT_WEAPON.ivaud must not be larger than the original. The recorded gun sounds are fairly long, and by cutting out their long echoes, I managed to get the ivaud from 3 652 KB to 3 207 KB, which is actually smaller than the game's original. This fixes all the missing sounds, but you lose some of that realistic long echo.
You can probably be more efficient by trying to exactly match the original sound sizes.
how about changing the size for the weapon bank in waveslots.xml?