The other thing here, of course, is that the current hard limitation of converters is an issue in an AD converter, rather than in the DA converter. It's at
input that we're generally failing to capture much than 20 bits of depth. It turns out that that's plenty for recording, though, so it kind of doesn't matter.
Higher bit depth throughout the process after recording and through to mastering and release is of course useful to reduce rounding errors.
The key issue here is way back earler in the thread:
you lose definition, particularly the analouge emulation effects if you don't record, mix and master at 64bitf
This indicates a very big misunderstanding of what is going on.
Firstly, recording. Presently, you
can't record at 64bit. You can create a 64 bit file while recording at approximately 20bits if you like, but that file contains no information that a 24 bit file wouldn't have done. Processing bit depth after that is handled by Sonar, regardless of the bit depth of the raw file.
As for mastering, absolutely every professional mastering facility in the world currently asks for 24 bit files, and delivers back 24 bit files, with the exception of CD masters.