a Power vs Volume Question

Does adding a powered sub to the mix free up the amp to play at louder volumes,ie: will the amp seem to play louder with the sub in line?

Shadorne;

If the "gain-sensitivity" on the amp has not changed with the addition of a sub, how than, can the amp play louder at any given volume? I understand, all things being equal, that the bass impact will be enhanced with the powered sub in line but how does that increase the "gain-sensitivity", and hence, the output of the main stereo amp? Thanks...

Was wondering if anyone could answer my question from above, it would be nice to know. Thank-you in advance...