If you have not had your hard gainer checked for parasites, that would be wise to do. You might consider increasing the dosage of PDG, but also trying some foods that may help with weight gain, including the Nurture™ and Optimal Performance™ you noted, as well as Epigen™ and the TNT™ products.
If none of this works it just may be that you have a naturally slim dog. If all else is well that is not a problem.
We do not have any information about the Angel Eyes products, but we have had reports of eyes clearing up with Archetype™ and Epigen™ added to the diet. You might also try the AddLife™ and EFA™ supplements.