My favorite preamp for digital playback is Grace M903. It's pricey but it combines state of the art DAC, headphone amp and volume control so that you don't necessary have to get a good quality CD-player or transport.
CD Direct to Mono Blocks or Preamp???
I just purchased a Pair of Dynaudio Sapphire's. I power them via Bryston 7Bst's. I'm running a California Audio Labs CL-15 (variable audio out) directly into the Brystons. I feel the Cal-Audio is the weak link and trying to decide to either replace it with another (better -suggestions??) variable out player or add a preamp to the cal (maybe still replace the Cal anyway but won't need variable out. My audio taste tends to like DETAIL !!. Appreciate your input.