The power amp i find can add some weight to the bass , some more umph in dynamic passages etc - but i find i my experience that the pre-amp and interconnects play a greater role in " changing the sound " . Of course it all starts with the source - album - cd - digital file , then the signal path etc . But i have heard and felt changes in tonality , clarity , soundstage , depth , detail with preamps changed out and keeping same power amp , and similar effect with cables .
This is not super hifi i am using as reference , but amps and pre amps , in the 3000-5000 per unit range and cables in the 100-500 per meter range .
power amp plays a role - but more in the dynamics and depth and breadth of soundstage .
Im on the hunt for new hifi now and considering a mix and match of components .
Speakers , oh my , a whole other conversation lol .