You only mentioned shampoo, are you using a conditioner at all? If not, that's your problem

. I have the Pet Silk Serum too and I have to say, I'm not crazy over it, I honestly don't see much results. The conditioner does a much better job than the serum IMO, guess it depends on the coat type though?
Is the Italian product IV San Bernard? Their PEK conditioner is suposed to be amazing, I'm going to be ordering it soon.