MaltLicker - Just DME to prime the keg. I do push out all the sanitizer with CO2 to purge the oxygen and minimize oxidation; but beyond that, I don't add any CO2 other than to serve the beer. Unless of course the beer is flat, which happens from time to time. I have never noticed any sort of krausen, except the one time I used a champagne yeast to carbonate a belgian tripel. It was minimal, and didn't affect the serving process too much. I poured about two pints of pure yeast when I first tapped the keg and the rest of it was beautiful.
Darin