Well - I talked to my vet.
Her opinion is he may have Gastritis again. (He had a case of this as a pup shortly after being neutered.) She's prescribing Flagyl, the medication he was on the last time and it worked, for 10 days.
She said if this doesn't help, he may have Inflammatory Bowel Disease. We'd have to do some additional testing to confirm that if the Flagyl doesn't help. If those results came back positive, then he'd have to be on a hypoallergenic diet and medication for the rest of his life.

Here's hoping the Flagyl works because Edan's only 3 years old.
I was also told to keep him on the Eagle Pack food for now but supplement it with white rice, pumpkin, sweet potato or wheat free pasta - basically some sort of starch. This will help keep the variables we are looking at to minimum. Throwing a new food into the mix at this point will just make it harder to pinpoint the issue.
She's going to leave extensive notes of our discussion and plan of attack for this issue for the vet that saw him a week ago since she'll be out on Maternity for the next few months.
I love my vet because she really is very patient about answering questions until you are comfortable with the situation.
Thanks for the suggestions everyone. Right now, I think Edan, his Dad (Celtic Fire) and I just need some prayers that we find the cause of this problem and heal whatever has his digestive system in an uproar.