Xenia, I'm also sorry you didn't get the answers you were looking for. At the same time, the ultrasound report did not show any awful abnormalities either, so that is a good thing.
I'm a little confused as to why the K/D was prescribed rather than a hepatic diet. (Royal Canin makes a decent hepatic diet.) Were Scooter's kidney numbers (BUN - Creatinine) elevated? I know he had proteinuria. Was a UTI ruled out, which can often cause proteinuria? The diet thing confused me because liver diets are generally low in fat, and kidney diets are high in fat. If it's actually canned K/D you are feeding, you can slice it right out of the can into thin slices, bake it in the oven at 350 until it's crispy (20-30 minutes), cool, then break into treat sized pieces and use as treats. The pieces should be stored in the refrigerator in an airtight container. Many veggies and fruits are both liver and kidney friendly (green beans, sweet potato, leafy veggies like kale or spinach, small slices of peeled apple (no seeds), watermelon, etc), but if your vet said nothing but K/D, I'd be inclined to stick with that until you had the retest in a few weeks, which is a great idea.
Did your vet suggest Milk Thistle or Denamarin as a supplement for the liver?
In the ultrasound, it mentioned cholangiohepatitis. Hepatitis just means inflammation of the liver, and the cholangio is referring to inflammation of the bile ducts in the liver. Hepatitis is often managed with diet change, supplements like milk thistle or denamarin, and antibiotics. If there is inflammation in the bile ducts, Ursodial (generic for Actigall) is a good supplement but requires a prescription from your vet.
If your dog is eating and feeling well within himself, it seems like your vet is following a good course of treatment in changing the diet and repeating the labs in a few weeks. Funny thing about the liver numbers. One thing I noticed after dealing with liver disease in my dog for 14 years is that the numbers can climb rapidly, but also drop rapidly. You may see a huge change in just a few weeks.
Hope this helps. Sending good thoughts for your little guy!
Diana