You can look at it this way. If the CDP with variable output sounded more or less the same with or without a preamp X, you wouldn't need that preamp unless you have extra sources. Preamp makes a difference in sound, and it's highly subjective to say which way sounds better. My Unidisk SC for example has variable outputs. Without preamp it sounds crystal clear and airy. With McCormack preamp in the chain the sound lost 2-3% of the transparency and 5% of midbass, but other than that it sounded pretty similar than without. With CJ tubed preamp the sound went on a huge transformation. It sounds richer, deeper, larger, and overall more pleasing. If your listening preference leans towards warmer sound, you would like it with a tubed preamp. If you like clear and transparent sound, you would not want a preamp. If you like the transparency and still need a preamp you would want McCormack. So, it boils down to your listening preference and need.
connectng CD player directly to amp, good or bad?
Some CD players with volume control can be connected directly to power amp, bypassing pre-amp. Mark Levinson 39 and Mcintosh 301 can do that. When I mentioned this to sales reps at dealers, they were all skeptical. They said pre-amp/amp is always better or go for int-amp. I am not s sure. Mcintosh manual shows how to connect CD player to power amp directly and it makes better sense for me since I am not going to have any other source unit. If I need more later, I can always add pre-amp. Is pre-amp really necessary?