DAC or CD Player. Help!

I get the point of what people are saying with "synergy," but unless you live in an audio shop, who has the money to throw a grand or two here and there to determine which component of the many they read about is 'the one' to mate with components they already own? I have to conclude that a lot of what 'synergy' means is whatever the poster thinks sounds good at that moment. Until he buys something else, of course, at which point the synergy changes to that. 
PS: expensive cables do. not. matter.

Price of cable might not matter, but one cable can deliver better sound than another.  Cheaper CDP can sound better than expensive transport when feeding DAC.  That is synergy.

OP, if this is a way of asking if you should buy a dac or a cd player, I would personally recommend a dac in this day and age.  I can stream most of the music in the world through online streaming services and my own library through a dac that I can control using an app on my phone.

Everything in the audio chain can have an effect starting with the mastering of the original recording.  This is getting complicated, but even the phase noise of the clock generator in your cd transport/player and the clock used in your dac has an audible effect. 

Regarding synergy, there has to be some intelligent decisions made when selecting audio components.  For example if you don't like bright / harsh sound, you wouldn't pair a bright sounding dac with bright sounding speakers and use silver plated cables - ear fatigue nightmare!