For the purposes of not having to traverse Stardock's forums, I'll repost the solution to getting Dark Avatar updated properly in Impulse.
To make sure the 1.80g.103 Dark Avatar update works properly, go to this registry key:
Change the "exe" value to "DALaunch.exe"
Change the "Path" value to the FULL location of where Dark Avatar is installed on your PC. For most, I suspect it will be "C:\Program Files\Stardock\TotalGaming\GalCiv2\DarkAvatar"
If you do this, then perform the Impulse Dark Avatar update (from 1.80g.102 to 1.80g.103), it will take a split second to update. If you leave the registry hack as I descibe in my post a while ago, Impulse will think it is not installed, download the entire game again, and install it in the main GalCiv2 folder, really screwing things up.
After this, follow CariElf's instructions for uninstalling the beta for Twilight. The uninstall process via Impulse will remove the beta registry keys, so the 1.9 install will go smoothly.