Honestly, I don't think the problem is the food. Actually, I think you should reconsider free-feeding. Free feeding has often led to obesity (surprise surprise ), bloat, and, acutally, boredom with the kibble. I would HIGHLY encourage you to feed twice a day VS free feeding before you try a new food.

I feed CSFTDLS to Giselle and she adores it! She has always maintained a healthy 57-ish pounds and we're pretty lazy, LOL. Here's a link to free-feeding:
http://www.lucythewonderdog.com/free-feeding.htm

For most dogs, getting two meals per day is ideal. (Puppies and lactating females should get one extra meal per day.) Because dogs will often overeat, free feeding (leaving a full dish of chow out all day long) can lead to obesity, the number one nutritional problem for pooches today.
-http://www.pamperedpuppy.com/features/200409_feedingpt2.php
Free Feeding

Some dogs go their whole lives eating without a schedule, having food left out all the time. Several things can cause this to suddenly become a problem, though.

If you add another dog to the household, or another dog comes to visit, you'll need to separate the free feeder from the other dog whenever they eat. The free feeder will suddenly not have constant access to the dish.

Dogs can develop medical problems from going too long without food. The free-feeder dog is of course not aware of needing to eat every so many hours. As a result, these dogs become candidates for things like seizures from hypoglycemia.

Free-feeding dogs often become overweight or underweight after awhile, resulting in the need to adjust food amounts. You'll need to convert the dog to scheduled feeding then.

Some boarding situations will require that your dog be able to eat on schedule rather than free-feeding. This would be especially true if a friend or relative with a dog needed to keep your dog for you.

Free-feeding a puppy makes housetraining more difficult. When a dog eats on a regular schedule, bowel movements occur on a regular schedule. That helps you figure out when your dog will need a potty outing.

-http://www.veterinarypartner.com/Content.plx?P=A&A=1549&S=1&SourceID=47
So, my advice is stick to CSFTDLS if it's obviously working for you. Just feed according to a schedule and watch how much your *individual* dogs are eating. Remember, when you free feed, you're dumping around 3-6 cups in a single dish allowing your three dogs to pick and choose who gets most. As far as we're concerned, Sylvia could be eating 3 cups while your other two pups are eating a single cup each. Good Luck with Sylvia and update us on her condition!