Is less than 24 bits worth it?

Let's not forget jitter affect on resolution!
Both circuit noise and data dependent jitter can easily "disqualify" the significance of additional least-order bits in a 20+ bit system. The intrinsic jitter from the oscillators that control the coax or Toslink connection to the DAC can destroy any hope of resolving near 24 bits.

When the analog signal is finally created, both amplitude and phase inaccuracy create deleterious effects. Using 24 bit resolution, the last bit translates to a signal amplitude of about a 17 millionth of peak amplitude. You can get an "equivalent" effect if the exact timing of that 24 bit sample is off by mere nanoseconds (depending on the exact slope at the sample moment), which is nothing more than jitter. Jitter that can affect the difference in timing from one sample to the next is created by intrinsic oscillator noise in Phase Locked Loops (the thing that tracks and creates the internal clock) or by the very bit stream itself (a phenomenon called data dependent jitter). CDPs can be more successful than transport/DAC combos in addressing these effects. Both have a really tough job getting true 24 bit resolution.

Sorry Easy_e. Just trying to address Eldartford's question above...