You are currently doing as much as you can to identify the root cause of your Norway spruce decline as you're receiving on-site, hands-on technical assistance from professional foresters, entomologists, and plant pathologists. Unfortunately, Illinois has far less capacity than your home state of Minnesota with regard to technical forestry assistance.
All you can do now right now is wait for laboratory results and wait for additional input from your state forestry agency. It is also very important to remind you and our readers out that even the best professionals –- whether they are professional foresters, plant pathologists, botanists, ecologists, medical physicians, veterinarians, marine biologists, etc. –- are sometimes never able to positively identify the root cause of biological decline or mortality in living things. And as hard as that is for some people to accept – that’s life and that’s Mother Nature!
Best of luck!