Here's an example of the OP's situation. I bought a Schiit Aegir power amp which doesn't have a lot of gain on its own. I originally purchased a Schiit Saga+ preamp to go with it, which uses a tube buffer in a unity gain circuit -- it adds no additional gain beyond what the source outputs.
While it worked fine with most recordings, there were some recorded at a lower level in which having the volume knob all the way up on the Saga+ was short of the desired playback level. I ended up switching to a Lyr 3 preamp which has low gain (+3.5 dB) and high gain (+17 dB) settings. It turned out the low gain setting was all I needed to fix my playback gain problem for all of my recordings.
While it worked fine with most recordings, there were some recorded at a lower level in which having the volume knob all the way up on the Saga+ was short of the desired playback level. I ended up switching to a Lyr 3 preamp which has low gain (+3.5 dB) and high gain (+17 dB) settings. It turned out the low gain setting was all I needed to fix my playback gain problem for all of my recordings.