regarding the OP.....
The best pre-amp will add nothing to the signal.
Lesser pre-amps contaminate the signal with colorations at best, distortion in the worst cases.
JMHO YMMV
I am not on your level, but I disagree. I might be wrong.
Anything you add in will/might have some effect.
You can buy some nice passive preamps which are little more than volume control.
I have a few.
On the deck, I use a Benchmark DAC/Pre. In my opinion, it is very neutral. It costs me a lot though.
In my RedNeck Bar, I am currently using a Carver CT-6 which adds to the sound in my opinion. I have a tube pre on order to upgrade that system. I don't know if it will. Many of Bob Carver's stuff have a built in tube color to the sound, not to mention the "holygraph" thing.
The purest sound from a CD (or even some LPs) might not be the most pleasing.
All the stuff is run through all types of mixers before we get it. Some do a good RECORDING job and some do crap. So adding a slight change yourself is no big deal. Pure sound is "LIVE".
In my opinion, unless you have high end stuff made in the last couple years, the best bang for the buck is a quality DAC. Damn good ones can be had now under $500.
OO