I run a Digital Audio Workstation that optimizes the 1st cores speed and power above how many cores the CPU has. So having 12 or 16 cores doesn't necessarily improve the performance of the DAW unless the 1st core is substantially faster. I'm currently running a Ryzen 5 3rd Gen.. My motherboard is an MSI B450. What CPU would be a good upgrade for the money say $4-500.00 ?
You're situation sounds very similar to gaming where even multi-threaded games and simulators have one main thread that is central to the simulation and limits over-all performance of the app.
Ryzen 5000 clearly has the best IPC of all Ryzen and the 12 and 16 core CPU's have the highest stock clocks, therefore would provide the highest single core performance. A 5600X shares the much better IPC with somewhat lower stock clocks but you can enable PBO with curve optimizer and improve performance. Just be sure to run really good cooling as it's a serious improvement to boost performance and that's true whichever Ryzen you have, 3rd or 4th gen.
One other thing you can experiment with is disabling some cores or multi-threading in BIOS. That will improve thermal performance which should help the CPU hold higher clock speed. As has been shown with games it may not actually help with your app, though, as there are other execution threads being run by the OS or other system level apps concurrently. As with games, even your app may have other supporting threads in that mix. If the OS' scheduler has other cores to run those threads on they won't take away cycles your audio app could better utilize for it's main thread.
That's also why a 5900X might help more than just it's higher stock clocks...or even a 5800X, although it's a lesser value proposition. There are more cores to spread the "little" threads over and not slow down that main thread executing on the one core that matters most.