CD player straight into amps?

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.

I have had a Wadia 830, 850 GNSC, and now a Camelot Uther, all of which were run directly into the amps with great success. I used to own pre amps, like BAT, Sonic Frontiers, B&K, that were nice, but the sound directly seems more refined and accurate in the mids in my system.
Give it a SHOT!!!!

Unlike some of the other post-ers, I tried a Wadia 860 with and without a pre-amp, and I liked the "with pre-amp" version better. A dealer friend of mine explained some techno-electrical theory as to why one might be better off with a pre-amp, but I'm too dense about that stuff to know what's real and what's not, or to even articulate it. I can just say that the CD sound was cold and clinical and irritating in the highs (almost glassy) plugged straight into the amp, and was warmer and more "musical" (to my ear) with a tube pre-amp in the middle. Yes, I understand the theory that each thing you put in between the source and the speaker adds more error, but my ears tell me what they want, and I try to give it to them, theory notwithstanding, and they want the pre-amp, so they can have it. Trust your ears.

With my Raysonic CD128, my one experience running it into a passive linestage was pretty disconcerting. Sounded thin and threadbare, very much unlike the way the Raysonic should sound.