Al is right, my 64-bit idea is mostly fantasy :)
Here is the problem, in a nutshell, the problem that seems to plague **all** aspects of audio:
There are the Rules of Human Hearing/Perception, and there are the specs on paper. They are not the same- the specs on paper for the most part don't give a damn about human hearing rules.
Now I have gone off about this a lot in the Amps/Preamps forum and won't belabor those issues as examples. Instead, let's look at how the ear treats noise, specifically analog hiss: Normally, our ears employ a masking feature, IOW the presence of a louder sound will block the presence of a quieter sound to our perception. Hiss is the one exception to that rule. I suspect its an evolutionary thing myself- the idea that hiss is similar to the effects of wind in the environment is not that far-fetched to me.... Anyway, we have the ability to hear about **20 db** into the noise floor of an analog system.
(if the noise floor is not composed of hiss, but instead is harmonic or in-harmonic noise related to the signal, our ears will not penetrate that, and so that type of noise floor will define the limit of low level detail that can be retrieved.)
With modern tape, 1/2" format, this means that you have the possibility of a 110 db dynamic range, if you include the range above 0 VU, a range that digital does not have.
This simple fact explains why an analog system of rather modest noise specs can have more low level detail than the best digital systems -*even though it appears to be noisier*. Add to that the fact that digital systems use less bits to resolve lower level signals (IOW, they have loose resolution as signal level decreases, which is why the normalization process is so important in the production of a CD) and you have a great part of why digital systems **as they are** can't keep up with analog.
IOW, part of it has to do with how we hear, and for the most part digital audio has ignored that, which has been a common problem with audio in general in the last 45 years or so :( Put another way, analog just happens to work better with the way our ears work.