I think the input impedance of the POWER amp side is a huge factor. Some amps will never work with a DAC directly.
Berkeley DAC into preamp or amp ?
I've done some searching but don't see many comparisons of the sound of the BAD Alpha DAC fed through a preamp versus into the amp directly. I'm interested in the degree/range of digital attenuation needed with amps of various gain. At what attenuation level did sonic degradation (if any) become audible?