- The reports about lack of 24-bit capture were before we had WASAPI. It may be worth checking to see if selecting WASAPI as host can deliver full 24-bit capture. (I don’t have a 24-bit sound card so I can’t test this for you).
- Are you sure that Nero captures the full 24 bits?
- The old criticism about only capturing 16-bits related only to recording (capturing the audio stream) on Windows with MME or DirectSound. Audacity works internally in 32-bit float, so it is best to use 32-bit float as the track format (this is the default setting).
I think these two posts https://forum.audacityteam.org/t/device-list-when-wasapi-selected/37111/7 are saying that WASAPI host records true 24-bit from 24-bit hardware.
Use the latest Audacity 2.1.1 from http://audacityteam.org/download/windows.
Let us know about your own tests.