Which segues back on point. How would Nagra's tube-groomed but solid-state Classic DAC fit into this spectrum by treating all PCM as DSD?

When Nagra specifiy magnetic decoupling for their digital inputs, they're not talking of chip-based items but their own miniature wound transformers.

Trick question. Why does it take the Classic DAC nine transistors to do the job of one tube?

"We wanted a high-quality analog output stage that would let the proven digital part of the unit shine at a more realistic price. One step toward that goal was to simplify the power supply so that the unit can work off a single DC feed. The second was to design a super output stage with transistors. We chose military-grade parts individually selected and hand-picked for their specs. That stage is pure class A and  replicates a kind of operational amplifier with discrete topology. It has very high input Ω, is super fast and its output stage isn't push/pull but a pseudo triode created by two field-effect transistors.

"Then we use a buffer as super-low Ω driver without any caps. We use this special driver also in other products and it has zero voltage gain or negative feedback. Providing the Classic DAC with a super-low output impedance of 16/10Ω on RCA/XLR insures a perfect match with following gear and keeps bass tight and extended."

Achieving very low output impedance with tube-coupled outputs is a lot harder without a final transistor buffer.

This photo of Nagra's 2004 DAC documents the current Classic DAC's far more streamlined user interface and less laboratory looks. Inside the precursor then still was a multi-bit PCM not 1-bit DSD decoder.