Such a controversial subject. lol, yeah and you'll get 17 different opinions. That being said, it's true that it's all important and the weakest link suffers, but I think that your source/preamp are extremely important. If the sound quality of the waveforms are not there from the start, there is no way you are able to restore it by downstream devices (i.e. amp/speakers). Sure, you could compensate somewhat for a bad source by using different preamp/cables/etc., but it's just compensating/synergy. It's not really restoring the original quality. There can be combinations that work well, however.
The choice of amp is important, but does not affect the sound as much as source/preamp. Source/preamp are also more sensitive to type of power cord / fuse / outlet. Interestingly enough, my R&D and experience has shown that power cables and interconnects are extremely important. I have made an average amp/speaker system sound world class by using ultra-high end power and interconnect components (i.e. OCC Copper solid core, rhodium connectors all the way through, Furutech fuses). My opinion on order of importance is as below.
1-Source
2-Preamp
3-Power
4-Cables
5-Room
6-Speaker
7-Amp