I fully concur that even the tinniest drops in the noise floor can have substantial results, especially in the digital domain. I consider one of the greatest audio myths to be that once you have a noise level that in itself is inaudible at normal listening volume, then that is all that matters - mission accomplished so to speak. My experience has been completely different, hence my own personal opinion that it is a myth. Whilst noise in itself is inaudible even on a "DDD" CD, for instance, it is still possible to hear the effect the noise floor has on what we do actually hear.
I've done many experiments over the last couple of years with 16 bit noise shaping, for example. I've experimented with many professional products and dozens of combinations - all mathematically perfect in their own way but each distributing noise in different parts of the 20 - 20 Khz spectrum. And even though I would have to amplify the noise itself by around 30 dB to even hear it at all, even at normal listening volume you can specifically hear it effect imaging, timbre and PRaT. More noise at the low end, for example, reduces PRaT, makes the bass itself less clear, slightly compromises imaging and can make the high end sound a little edgy with slightly "forward" sounding timbres compared to the 24 bit master. Even out the noise across the spectrum up to, say 15 Khz, and the whole presentation becomes clearer, imaging is more solid and timbre closer to the 24 bit original. But some might find this sound to be less subjectively pleasing as it is not necessarily as "organic" as when noise is added at lower frequencies.
I have maintained for a couple of years now that trying to work within a 16 bit envelope is impossible if accuracy of timbre, imaging and PRaT are the three goals to be achieved. But once you get to 18 bits, it is amazing just how much difference those 2 extra bits make - to my ears at any rate. It is still no substitute for a typical 21 bit noise floor that 24 bit components often have, but it comes very close.
And this is why I was so impressed with the Entreq gear. It seemed to give me a couple of free bits. Not in the true sense of course, but in order to achieve the same sound without Entreq versus having it, I had to create 44.1 Khz masters at 18 bits instead of 16 bits. And I think that is very high praise indeed for Entreq. Sure, it might not be measurable as such, but as I have said earlier, none of us hear (or should hear) the noise floor anyway. It is what the noise floor does to the music itself that is the problem.
As an aside, in all my studies of digital noise and the effect it has on the music itself, I came to a completely independent conclusion that I d have been a very happy ever after audiophile had the CD standard been 18/48, even if that meant short albums (or needing bigger hands to handle the bigger disks!). It was only after I came to that conclusion myself that I discovered Decca's in-house digital recording and editing system was also designed to work at 18/48 as Decca felt that this was what was required in order to exceed the best analogue standards of the time (which by then included the use of Dolby A noise reduction).