I feed mine gamebird feed instead of layer and offer oyster shell freechoice on the side. This has worked great for my mixed species/age flock and seems to really help the hens get thru molting faster and in better health the was the case when I was feeding layer.
As far as the great cat food debate goes--I think as with so many things that moderation is the key. I have no scientific studies etc. to back this up, just my own experience. I've never used cat food as a protien boost, mostly because I find the gamebird feed works so well for me, but I have used wet cat food for ill/injured birds who are feeling so poorly that even scrambled eggs don't tempt them.
I'm sure the wet food made the difference between life and death for a rir hen that had problems with cocci after going thru a particularly bad molt (before the gamebird feed) when she was about 18 months old. She scarffed the cat food down like there was no tomorrow and within a few days her strengh and appetite and recoverd to the point that I was able to stop feeding the cat food and she went back to eating her pellets with a scrambled egg mixed in. A week after I thought she was a goner she was back with the flock.