And I am sure you are right. They were (and I believe still are) using NX300's which if I'm correct, those are pretty dated radios. Replaced by the NX5300. AFAIK they haven't upgraded anything on their system since last I spoke. I was never a user on the system nor did I ever listen to it so I couldn't tell you the kind of problems they were really experiencing.
The NX-300 is still available.
A good replacement for it would be the NX-3300, that radio will do analog and NXDN -or- DMR
The NX-5300 radio will do analog, and any two of the following at the same time: P25, DMR, NXDN.
If audio quality was the issue, that's a failing on the shop or whoever programmed the radios. Kenwood has documentation on properly setting up the audio on those radios. I have used their guide and the NXDN radios sound good.
In fact….
When I was trialing the systems, I had a MotoTrbo repeater and an NXDN repeater running. Comparing the two, MotoTrbo sounded crappy compared to the NXDN. Could have been the Motorola shop that didn't set it up correctly.
I run a couple of analog systems and an NXDN trunked system. Same dispatchers, same console, same microphones. In my work truck, I have a NX-700 VHF radio and an NX-900 800MHz radio. Talking with the dispatchers on both, NX-700 on analog VHF and the NX-900 on NXDN 800MHz, the audio quality is better on the NXDN when compared to 12.5KHz analog. That's same everything all the way through, with the exception of the repeaters. NXR-900 800MHz NXDN trunked system, VS. Quantar/MTR-2000 Motorola VHF.
It comes down to the skill of the tech setting up the system.
Unfortunately some radio shops sell the hardware, toss it up and walk away once they have the money in their hand. Getting them to return and fix issues can be impossible. Would be an easy fix.