The fix? Go buy the original system from a real radio company and pay 2.5 mil now because you waited. Give the other radios back and sue for your money back.
I hope you are not suggesting that if this agency had chosen Motorola radios they wouldn't have this issue. That just isn't true. What likely would have happened is that any Motorola dealer would have the proper tools to engineer the system before installing it. Suggesting that Motorola is the only company that makes good radios shows a bit of ignorance on your part, and I'm sure that isn't what you are trying to say. With a screen name like yours, I'm guessing you are a big Motorola fan. No problem with that, I like their gear too, but I have a fair amount of Kenwood gear also and neither brand is better than the other.
The issue is that going from a 25KHz channel to a 12.5KHz channel results in a loss of coverage. Doesn't matter what brand radio you are using, Motorola or Kenwood it's just the way it is. Any salesman that tells you otherwise is not telling you the truth. Going digital likely can help a bit, but not enough to overcome the loss in coverage. By going back to the "old" system, they likely went back to 25KHz analog channels.
Any radio shop worth it's salt should have known this and properly designed the system, or at least controlled the customers expectations. Sounds like that didn't happen. That is a failure on the radio dealers part, not Kenwood. Suggesting this is Kenwood's fault isn't accurate, although maybe they need to do a better job of picking and choosing who their dealers are. Sounds like this dealer is giving Kenwood a black eye. I'd be surprised to see if they are still a Kenwood dealer when this is all over.
As to the radios selected, our PD is using Motorola MTS-2000's, XTS-2000's Kenwood TK-5210's and NX-200's. Our fire department uses all Kenwood gear, including the TK-5210. If you don't think these radios are capable of performing the task, you'd be up against a lot of agencies, including CalFire, that would disagree.