They say that in just about every breath. Here is Schiit on modi multibit:
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Exact level implies 100% fidelity to audio samples. There is no talk of screwing them up to make them sound better.
That statement from Schitt is completely misleading and a gross misrepresentation of what bit-depth means in a DS architecture.
As for multibit accuracy to 20 bits or more, it can be achieved, but DS designs have so taken over that it is just not worth the effort and cost in manufacturing and test to do so. And the whole linearity argument glosses over the fact that there have to be components in the output chain of a DS DAC that are accurate to 20+ bits; delta-sigma is not a complete panacea. It is about noise shaping, mostly targeting the quantization noise, but linearity must still be achieved to keep the distortion low. There is a lot of trimming and processing circuitry on those chips to achieve such high performance. The final demodulator must achieve high linearity and have good power-supply rejection and so forth or you start amplitude-modulating the bit stream and that will show up in the output.
There always seems to be a nostalgic "the old stuff was better" group around and I admit at times I am one of them. But a lot of times it is misplaced. Multibit DACs may not suffer from noise modulation but correction circuits in the very highest precision ones I have seen (30 bits) include -- gasp! -- delta-sigma modulation techniques and high-speed internal clocks to do random bit swapping and play other games to achieve extremely precise element matching. Large unary arrays for the MSBs (using a large number of unit-value cells. e.g. the upper 6 bits of a 16-bit DAC may use 64 cells instead of six, reducing the matching requirements by roughly 1/64) improve linearity but now you have more noise, more control circuits, and a much larger load for the buffer to handle. The large area means process, voltage, and thermal gradients across the array are more problematic. Etc.
My grandmother used to say that the young folk pining for the good old days didn't have to live through them. I miss her blunt wisdom.