I don't know whether the original poster is still watching this thread, but if so, just to clarify: There are numerous preamps (including pricey professional ones) that are designed and sold on the basis of having a particular sonic "character," which is really a form of euphonic distortion. These preamps are used for pop and rock music recording as "sound shaping tools," and people can become quite fond of their favorites and partisan about them, though naturally what kind of distortion you like to hear is a personal matter.
Many tube preamps fall into this category nowadays along with some solid-state units. But it is entirely possible for a preamp to have so little sonic "character" (distortion) of its own that it is effectively neutral and transparent--simply taking the signals that are fed into it and making them larger so that they can be passed along to a recorder or some other piece of equipment.
That end of the market is smaller because its main customers are classical music people, and the classical segment has done little but shrink in recent decades. Plus from a marketing standpoint, if you have a product with the "flavor of the month" you can sell it on that basis, but there is no "flavorlessness of the month." So "neutral" sound gets just one market niche, while each type of distortion that its purveyors can name will have a niche, too--guess who gets all the shelf space. (That happens with microphones as well.)
My point is that if you find a suitable, neutral-enough-sounding preamp, you will soon find that almost every other variable in the recording setup will matter more. Moving the mikes one foot higher or one foot closer or farther away will matter far more than the miniscule (for most listeners, absolutely undetectable) difference in sound between Millenia and Benchmark, for example. The quality of the equipment only gets you to a certain level of potential, and the preamp is the one part of your setup which ought to have the least audible effect if it's working the way you want it to.
--best regards