Well, layer feed is an option during laying season (for some, I know, that is year 'round).  It has extra calcium, and probably protein and calories.
I understand that it is, in fact, a little tricky with a flock of drakes and duck hens, as too much calcium for the drakes is not healthy (too much calcium for any non-laying duck is not healthy, I am told).
One possible way to deal with this, and I make no guarantee, is to offer oyster shell free choice during laying season.  Perhaps the drakes would have no interest in it.  You could also supplement for calories and protein by offering extras in their food (there are a number of things that can add healthy calories and protein).
When I shifted my runners to grower / maintenance feed, they shifted from crumbles to small pellets.  They do fine, and they need abundant water when the feed is available to them.  They do sometimes grab a big mouthful and then make a higher pitched honking, dry cough kind of noise, then wander over to the waterer and wash it down.