High end stereo preamps? Worth it?

@mitch2,@emergingsoul

The only case where I could think of mismatch issues between DAC, attenuator and power amplifier are impedance related: low output impedance on the DAC, high impedance inputs on the power amp or very poor choice of interconnects. This is however an unusual constellation that one normally needn‘t be overly concerned about.
Where you do get a problem is when you rely on a DAC‘s digital attenuator; for the avoidance of doubt all digital output levels should be set to max. In other words: an analogue attenuator or volume control in the DAC is always needed

@mitch2 

I was obviously referring to analogue sources, not DAC outputs

You don't need analog volume control it can be done in the digital domain. You don't need a preamp in a totally digital system. 

I used passive preamps for many years. Then one day I decided to check out an active. I decided on an Audible Illusions. I was stunned and amazed! The music had structure and substance I never heard.
I now have upgraded to an Atma-Sphere MP-3. Pricey but well worth it.

The music had structure and substance I never heard.

You probably heard tube microphonics/euphonics.
If you put that same source "direct" into a pair of very expensive headphones you will get the sound more similar to the passive pre than the tube. A tube cannot make music it can only amplify and in this case "color it"

Cheers George