I once started an archived thread basically about this topic, check it out at Ever Perform A Preamp Bypass Comparision Test? if you are interested...
The Truth About Preamps
I'm wondering now that we're in the digital age with so many cd players having variable outs, what does a high quality preamp do for a system? I've heard so many different stories on either you get more detail straight in or that you get more bloom with a preamp. I would think that if you had a musical cd player such as a Cary running straight into a musical and smooth amp such as a Classe or Conrad-johnson you wouldn't need a preamp...all this given you have only cd as your source...I'm just wondering what you guys think and your experience running a cd player straight into an amp. I'm thinking of running a Theta Miles straight into a Classe CA-300