In the publication’s DAC published tests the reviewers almost always tested the DAC connected directly to the amplifier. I think I understand why—nothing in the chain influencing the DAC sound. Is that the correct assumption?
No. It’s very system dependent, but in my experience most systems benefit from a good preamp. A lot of amps just need the added boost from a dedicated preamp to be driven optimally, so that will be of particular importance to pay attention to.