@ozzy - While the majority of passive preamps are attenuators (with 0 dB at full clockwise position), some passive preamps (namely transformer or autoformer volume controls) do provide gain, but not a significant amount.
@sarsicism - To answer your question in simple terms you are trying to achieve the proper gain structure from your source to amp. Most digital sources put out 2V output which is enough to drive most amps to clipping. So a preamp with low or no gain might just be enough for your system (or a digital source with volume control). How low a sensitivity are we talking about with your speakers? Do you have an analog source like a phono stage as well? With analog sources you almost always need some additional gain in the system and the preamp is the most likely place to add it in. I have run analog sources successfully through passive preamps, but today I use a preamp with 20 dB of gain because my two analog sources require it.
