My preference is for a DAC/Pre and the new RME ADI-2 unit just released offers full preamp flexibilities in a single half-rack space. Also have an Emotiva XMC-1, which is brilliantly designed/based on a Linux computer, and use it for a 5-channel control box where it works fine. The converters, however, are far less accurate than the RME ones.
Disagree with phomchick's assessment of DACs over $800 sounding the same. Currently have over 10 DA converters (home and studio) ranging from Oppo, to Audient, to Emotiva, to RME and find they all sound different. The amount of difference depend on how good the rest of the system is (and especially speaker quality). The newly-released RME converter has made a large improvement in my stereo system -- all reviewers and owners have noted its startling realism. Sadly, they are VERY hard to get -- RME misjudged their appeal and has not been able to catch up with production.
The Preamp question is also impacted by computer capabilities. JRiver allows you to add plugins to its DSP Studio. For a number of years have used apQualizr (a German app) in conjunction with REW to tune my stereo room. It has impressive EQ capabilities but is not ergonomic. In the studio world, the standard EQ plugin is FabFilter and it is worth the price (about $180).
Think we are headed in this plugin direction for all room correction and DSP functions and believe it is better handled there in order to achieve the best audio quality.