Is the preamp the “heart” of the system?

The preamp May add colorations, be less pure, add distortion, etc, etc...  I don’t particularly care.  My desire is to have an engaging and enjoyable system that delivers an extraordinary listening experience.   The “purer” the sound tends to be the less engaging on many recordings.  

You are correct compared to going amp direct, or using a "good passive pre impedance matched, an active preamp will add coloration's, distortions and also have less dynamics. 
If you need this from an active preamp give this to your sound, then I say do something about your source to fix the problem, and then flick that expensive active preamp altogether.
The old saying continues to be correct "the best preamp sounds like a piece of wire", guess what that's what going direct sounds is. 

Cheers George

coming from a cath lab background, the pre is the Brian’s of your system and the amp the heart or power.  Pre makes decisions and the amp will follow. But in the end, who cares what normanclature you use to describe your system, just enjoy and follow what your looking for in the end.

Pre makes decisions and the amp will follow

Ho dear!  and if the pre is not totally transparent and free of distortion as the best pre in the world is "suppose" to sound "like a piece of wire" it's said. Then it's coloring and distorting the sound of the source.
For it to sound like a "piece of wire" it would then sound like the source direct to the amp.

Cheers George 

YES

Yes, yes... a straight wire WITH GAIN!
Passives mostly have the straight wire part but not the latter.
But “uncolored” is highly subjective. I think that preamp manufacturers all have their own idea of what music sounds like and embues their pre with their “house sound”. Or “no sound” if you will.
But no sound is not necessarily desired. I think the safest and, hopefully, the best choice is to match the preamp with the amp by using units of the same manufacturer. I have found an amp in which I love the house sound, Atma-Sphere. I believe it is unique and special. So, I want to emphasize that sound by using an Atma-Sphere preamp. I think and hope that this match will be my destination units. And the amps work great with my speakers. Off the merry-go-round!