Impulse don't support store CDs except on GalCiv 2 I think. Not even GalCiv1+ Altarian Prophecy cds I got long ago will register properly. I was more worried about Space Rangers 2 though which I bought a few years back. Needless to say, after a few emails I was told sorry for my troubles, they don't support CD's but planned to implement it in the future.
Now, the support I do have with the games I bought on Impulse got me to stop cheaping out and pay the full $40 for SR2: Complete. That way each time I want to play Reboot I don't have to find the old DVD and install it in a certain way to run with Reboot, I'll just download Impulse and be done with it. Sorry if that's not the answer you're not looking for.