one thing to try (majorvices helped me with this a couple years back) is to hook the gas up to the beer side and bubble the CO2 up through the beer - will help release some of the sulfur.
That's how I always carbonate my kegs. I really didn't smell sulfur when I purged the gas a few times so I think its going to be fine.
[I'd recommend no more than an oz. of carafa. I've switched to Sinamar for coloring alts and prefer that to carafa.
I avoided it entirely this time. Its not the roasty note is overwhelming or unpleasant, I just think it is out of place for the style. I may get some sinemar, or at least add carafa late in the mash if the color is needed.