Yep, I'd say Jim has the right idea here. The problem isn't a JRiver Media Center problem at all, but a hardware limitation with the M1 Apple Silicon SoC with HDMI. The M1 is limited to and can only output 48 kHz via HDMI, so all other sample rates need to be be resampled to 48 kHz for it to work correctly. VLC and Apple Music works because the system is automatically doing the resampling in the background without informing the user (you in this case). It looks like it's a limitation of the M1's chipset, and hopefully it's something that Apple addresses with the M2. But since your downstream hardware doesn't appear to support 48 kHz, you're at a bit of an impasse here.
Usually to workaround the issue you have to resample everything to 48 kHz by going to DSP Studio > Output Format > Sample rate and setting all sample rates to 48,000 Hz. However, if your downstream hardware doesn't support 48 kHz and it has no option to resample on its end, unfortunately adding something like a USB DAC is likely the best option.
