CD player straight into amps?

Actually, there are several threads on this very topic:

http://forum.audiogon.com/cgi-bin/srch_fr.pl

Sometimes threads are difficult to find. However, to summarize. . . some prefer a preamp and others prefer the CDP directly into the amp. It may depend on the quality of the volume control, etc. I am running an EAR Acute CDP directly into an EAR 859.

I'm listening to a Linn Genki running directly into a Linn LK-85 right now. Sounds great. I've read here that a higher end Linn pre would improve the sound. No hurry here.

Not all CDPs/External DACs come with volume controls.
Not all volume controls on these are of top quality either.

Its easy to say no preamp is the best preamp but each system is different and you need to decide what works best for you.

A friend of mine has a Bel Canto Dac 3 which has a volume control but still prefers to use it with a Bel Canto Pre3.

If you can run it direct then why shouldn't you try it !? At least you will learn how good or bad your pre is, or what you like or not about your pre. It learns you to understand what each component adds to the whole.