The best preamp, to my ears, has been a dedicated ditto integrated into the DAC; that is to say, no separate hardware preamp in the traditional sense. With the power amp used (Belles SA-30) the matching to the DAC/preamp (SOtM sDP-1000) is very successful, and with not a flicker of the "anemic and drained/non-dynamic" sonic imprinting the DAC-direct solution has often been reported having. Matching obviously is paramount, but newer solutions of dedicated DAC/preamps have come a long way making named issue equal zilch, and thus matching is less of a problem. Volume controls also have come a long way via digital implementations these last years, though the one used in my SOtM DAC/preamp is in the analogue domain (digitally "actuated").
Much of the controversy/debate over whether to use a separate hardware preamp (when we disregard its necessity with turntable setups) or not (i.e. as integrated solutions with only a digital source) seem not to take fully into account how systems can be build from ground up via either one or the other; in my case I've intended the latter from the beginning as an outset that would then come to fruition, and as such the inclusion of separate preamps often tip the balance in my setup where very often a lack of transparency and oddly "flavored" signature sneaks into the sound. Very expensive preamps have sometime blurred which solution to choose, but where this has occurred my thought has always been that the expense would be better invested elsewhere.
Conversely where separate hardware preamps have been used as an outset in ones setup(s), it's easy to imagine how its negation could induce sonic alterations that stem from the balance of the setup as a whole, and thus might call for rigorous tweaking to come near ones preferred sonic balance sans preamp.
