The most important piece in a stereo system???

It's all equally important. The single most important thing is that all of the components work well together. From the breakers feeding the outlets power to the window treatments in your room to isolation and everything in between. WATT/Puppies are great ... but coupled with the wrong amp (even a very expensive one) will have trouble surpassing a system a tenth of it's price. Half a dozen 'little' problems in your system/enviroment will cause just as much sonic havoc as a bad component mismatch.

I basically agree with swamwalker...front end,dac/cd player! Having said that...room acoustics also play a major role in overall final sound quality.

Quality of recording and room are absolutely the most important. On the specific system components, the pre-amp per Gregm's and other comments above.

It's a little bit like asking which is the most important link in a chain. In your system it is the weakest link. Admittedly, each chain in the audio link is different. I disagree with the comment above that "good speakers accurately reproduce what they are given." I am far from a speaker expert but I have made about 20 pair and all speakers color sound a great deal. They have a really amazing job to do. A Loudspeaker is a compound transducer. In conventional speakers electrical energy is transformed to magnetic energy, magnetic energy is transferred to mechancial, and mechanical energy is transferred to acoustic energy. Every step introduces distortion (disorder). It will be this way until they repeal the law of entropy. Don't hold your breath. No speaker simply reproduces what it is given.

The frontend. Everything flows from that.....just my opinion. The other views here all valid too. We all try for the end result..music, music music. Good question, perhaps no definate right answer.....they all have merit....regards, Bluenose