As you read through various forums and reviews, there are plenty of people that prefer no preamp...and maybe just as many that prefer the sound with a preamp (let alone some convenience switching issues)...and each with various descriptions of the sonic advantages...so maybe no clear cut winner here, just personal preference, I'm not sure...I use a preamp, I like the sound?
The issue of DC coupled is maybe more interesting. Pass Labs well respected XS preamp lists specs of:
Frequency Response -3dB @ 2 Hz and 60 kHz
Input Impedance 42k balanced
Output Impedance 120 Ohm bal, 120 Ohm SE
CMRR -65 dB, 1 kHz
Cross-talk -100 dB, 1kHz Ref 1V
Signal to Noise Ratio < -110 dB, Ref 5V
So, not sure if the Pass XS is DC coupled and if not, does it matter given how many people seem to like the sound...again????
Benchmark (pretty much the darling of ASR for their great measurements) shows a phase spec at 20KHZ for their DAC3 HGC:
Inter-channel Differential Phase (Stereo Pair – any sample rate) +/- 0.25 degrees at 20 kHz
Inter-channel Differential Phase (Between DAC3 Units Fs<110 kHz) Any sample rate. +/- 0.25 degrees at 20 kHz
Is this DC coupled...and if not, did it matter to their measured performance numbers?
OK....so what is my point?
If you take the crowd at Audio Science Review....they seem to be pretty focused on numbers implying that the numbers directly relate to the quality of the sound.
If you take the Audiogon crowd, they care about numbers but the numbers don't determine the sound quality...the sound quality is much more a function of the tuning by the designer and the interactions with other equipment (and for speakers, the room)
Personally, I'd like to see more correlation of numbers to sound perception...even though this in itself is imperfect. This might tell us, is DC coupled audible to most people? Or is THD + N = 115db audible to most people : and does it sound "better"?
My sense is that Tommy has it right....you need great numbers but you also need tuning to the final "best sound"....and if you don't happen to prefer the designer's final tuning, well that is a different story.