[pcc]

A significant factor, which is perhaps not brought up often enough, is the implicit assumption that everything is always going to be 100% linear.

In the textbook case, more than 16 bits per sample might just seem to lower the noise floor. However this is based on the assumption that the voltage spacing is exactly the same for every increment in the sample word -- and this is simply not going to be true in the real world.

This applies to both axes: at 44.1kHz, no clock tick is going to be precisely equally spaced from every other.

In other words, every A/D and D/A process is introducing non-linear behaviour and thus artefacts that change according to the actual input, as a concern quite outside that of the noise floor or the Nyquist limit.

Increasing the bit depth and sample rate helps reduce the effects of such non-linearities.