My two cents here:
1 Room
2 Speakers
3 Source
4 Preamp/Power Amp (depending on speakers, a good integrated with few watts can be enough)
5 Power cords
6 Speakers cables
What makes the biggest difference in sound quality?
When making changes or adding things to your system, what makes the bigger difference in sound quality on preamp‘s and power amps? Interconnects, speaker cables, power cords, or fuses?