Yap, the declared 24 (or even 32) bit resolution cannot be perceived by humans. The best DACs can reach around 20 bits, mine is a very good DAC and reaches slightly less than 20 bits. This is due to the quantisation noise, which masquerades everything beyond 20 bits. In other words, in the best treated rooms with the best rigs, you can get the leftmost 20 bits of each sample of digital audio.
This is the reason why I do not like the digital volume and opted for a good analog passive volume control. Jriver has an extremely good digital volume on 64 bits. However, only the leftmost 20 bits can be actually heard in the best acoustical environments. Drawback is that each approximately 6db of level reduction means that the bits are shifted to the right by one position. Since only the first 20 bits can be actually heard at most, this means that for low-level volumes the first, say 5 or 6 bits are always zero, and thus the leftmost 20 bits contains only 15-14 bits of audio signal that can be heard. This is even less in normal rooms, not treated professional studios. This means that the low-level details, such as ambience and 3D soundstage, are getting lost, which makes the difference in hiend audio.