Can Adding a Preamp (where there currently is none) Improve SQ?

See, it sometimes just sounds better somehow. Cascading the two amps cannot possibly change the overall dynamic range and still be linear. But you can drive the power amp into soft saturation of the peaks in order to enjoy more exciting mid level response. This can give the impression of greater dynamics or "slam" because we don't notice the clipped peaks if they are infrequent and soft enough, which is something a tube power amp excels at.

Weird as it seems, an active line stage preamp actually spends most of its time attenuating the signal. That is, the output from the preamp is less than the input. Unless you are playing near full volume. Maybe we should call it an active attenuator?