I ran into a bit of a problem and didn't see the solution in a sticky but it seems that it would be a common problem (since I followed a pretty basic path, nothing complex).  Here are the steps I took along with the solution to the problem in case anyone else runs into it.

1. Downloaded/Installed Impulse.
2. Used Impulse to purchase GalCiv II: Ultimate Bundle Pack (Digital Download).
3. Got invoice e-mail with the 3 Serial Numbers.
4. Tried to download / install all 3 games via Impulse.
5. GalCiv II download started correctly but the two expansions did not.  They said the registration information was wrong.
6. When I selected one and clicked Edit Registration on the right it took me to a list of my registered products and GalCiv II and both expansions all had the same Serial Number listed.
7. Changed both expansions to use the Serial Number I recieved in the purchase confirmation e-mail.
8. Went back and told both expansions to install.  They now both are downloading.