Which is the most important part of a stereo system?


My system consists of a pair of B&W 630's, an old Denon 50 watt reciever (DRA-550) from the mid 80's, a Marantz CD5004 cd player, and now a Pro-ject Debut Carbon DC Turntable.  I'm pleased with the speakers and the cd player and while the Denon sounds good it has some issues and I want to upgrade.

I'm planning on returning the Pro-ject TT and getting a higher end TT.  I'm also looking into getting a new amp pre amp with a internal DAC.

Is the source the most important? The speakers? 

Please Help!
klimt
I’m agree with roberjerman. The source is very important, but all the little things are very important, cables to. Don’t forget the speakers: everything has to match..  and than finding like a puzzle, the best pieces. Sometimes a lot of work to find the right “click”. Enjoy your music!!!
Too hard to answer. Every component is critically important. Without one, you have nothing.
Here is my prospective on what's the most important part of a great sounding hifi system.
You can easily find excellent source, or amplifier, or speakers or cables.  However, there are not so many good sounding preamplifiers and they make enormous difference for the quality of sound, even if you only use digital source.