In order to get rid of the pre-amp, I think a few conditions need to be met:
1) high quality parts for the attenuator at the CD/DAC output
2) enough muscle/high quality parts in the DAC analogy section to drive the cable and power amp.
3) Good cable that's easy to drive
4) Easy load at the power amp end.
I personally consider a Pre-amp is an outboard attenuator + extra muscle to drive the cable and power amp.
In my experience, no pre-amp is always better than a crappy pre-amp; a good pre-amp is always better than having no pre-amp.
But then I have never tried super high quality passive pre-amps.
1) high quality parts for the attenuator at the CD/DAC output
2) enough muscle/high quality parts in the DAC analogy section to drive the cable and power amp.
3) Good cable that's easy to drive
4) Easy load at the power amp end.
I personally consider a Pre-amp is an outboard attenuator + extra muscle to drive the cable and power amp.
In my experience, no pre-amp is always better than a crappy pre-amp; a good pre-amp is always better than having no pre-amp.
But then I have never tried super high quality passive pre-amps.