I think the most you can expect from a preamp is that it mitigates some limitation in the connected equipment and in all other ways is transparent.
Most of the time a preamp is there for the convenience of switching and having a single control to adjust the volume.
As @atmasphere pointed out an active preamp might act as a buffer and present better impedances than if the components were connected directly to one another. And I agree with @almarg in that a very good attenuator in a preamp allows you to leave all source equipment volume controls at max which will improve the sound.
If your equipment is well matched with top quality attenuators and you don't need the convenience then I don't think you'll get much out of a preamp.
Most of the time a preamp is there for the convenience of switching and having a single control to adjust the volume.
As @atmasphere pointed out an active preamp might act as a buffer and present better impedances than if the components were connected directly to one another. And I agree with @almarg in that a very good attenuator in a preamp allows you to leave all source equipment volume controls at max which will improve the sound.
If your equipment is well matched with top quality attenuators and you don't need the convenience then I don't think you'll get much out of a preamp.