Dick Olsher has posted a review of the Monarchy Audio NM24 preamplifier-DAC ($1590) at The Absolute Sound. His conclusions:
“First, there’s still plenty of audio magic left in Burr-Brown’s 24-bit/96kHz PCM1704 chip. Second, a tube buffer is sonically superior to an op-amp-based buffer, as can easily be ascertained by auditioning both built-in buffers. Third, it is much easier (i.e., less costly) to design a good-sounding DAC using an R2R chip than it is to deploy the currently ubiquitous delta-sigma type. Its sound character is exceedingly analog-like, as the NM24 sidesteps the halo of brightness that permeates the harmonic textures of so many delta-sigma-based DACs.”
You can read the full read review here.