I know the HDMI audio driver for Raspbian / DietPI was truncating bit depth to 16 due to the driver source being compiled to utilize only S16_LE, but can anyone confirm it’s still operating like that? I haven’t seen any posts about it in the past six months.
It’d be nice to use the built in HDMI audio out if that’s fixed, but otherwise it looks like you’ll have to use an external transport like a Hifiberry Digi+ or external USB DAC.