Bass management is a multichannel term, not 2 channel. The "management" portion derived from the fact that not all speakers in a 5.1 or 7.1 setup may be identical or capable of putting out a full range signal; it was up to something like a pre/pro receiver or black box (ICBM) to route low frequencies to those speakers or subs that can handle the load.
In 2 channel the low frequencies are either handled by the full-range stereo pair or a subwoofer, if needed. That sub is either crossed over with the mains (active or passive) or run in parallel. Period. No "management" needed, other than a crossover filter (high pass, low pass), usually included in the sub.
So when you ask about 2 channel preamps, don't mix metaphors and ask about bass management or other HT issues (speaker distance, etc.). A stereo preamp is the heart of a 2 channel system that consists of more than one fixed level source, be it a turntable (with associated step up device), a cd player, the 2 channel audio output of a DVD player, a universal, and yes, even a computer-based streaming device (cuz many computer-based sources only attenuate digitally, a potentially noisy and bit-reducing solution if not done right). However, if you have only ONE source, and it is ONE variable-level source, like a Squeezebox or Transporter or PC with a decent soundcard, then of course you don't need a separate preamp....your source includes one on it's innerds. Just hook it directly to the power amp and make damn sure the volume is down or is not set for "fixed" when you power up.
Personally, I love the sound of my tubed Modwright LS 36.5, and have too many sources to go without it. In includes the necessary HT bypass so that when I use my processor for hirez music or movie processing then the stereo preamp "gets out of the way" and simple acts as a signal path to my front power amp, volume attenuated by the processor.
"We're all bozos on this bus" - F.T.