I just read through this quick, so sorry if I repeat too much of what was said.
I agree with the post above, you should mix your food. I work at a kennel, anytime we have a new food. For example, we got a huge donation of food from purina or some company, so we mix it into the food they've always been on.
If you are trying to find a brand that is of a quality you want your dog to be on and that he will eat, maybe try sample bags? I'm sure you could easily get some if you emailed companies and asked for one.
Also with the dog trying to get table scraps, you just have to show him that is not ok. Whether you would want to train him with that or just push him away. If he jumps at you when you get up with a plate, you can always lift your leg as a block, well block with your knee. They usually get the hint with that..don't kick, just block.