Do preamps enhance sound quality?

I recalled a designer introducing valve or other into the CD player to offset the electronic tone and some now use " plug In " software capsule to return the tonal effect to a more palatable natural sound.

Then there is the high output of CD /DAC  players that accentuate the "bright glare ".  I see from my less than knowledgeable perspective, that even the new generation brought up on Digital electronic computer generated sound who have lived to hear a Saxophone or Contre -bass or Violin in a live set Up and then return to their CD player to be dismayed, the " feeling or emotional content' is not there in it's vivid content. 

I see a Pre -Amp necessary to attenuate the CD ' output and yes Music is Created in a medium of Communication and it's authenticity and originality is the value of the ' Art" . But , the artist and his " piece of creation ' is under the spell the Sound Engineer and electronic  Mixing Console among much hardware and Software before it reaches the Listener in appreciation of the Creation. But listening to a specific piece of music on different " audio system" provide a different take or taste and the Listener consume according to the " Perception" he chose or has develop in his Psychy and if as mIne in Acoustic instrument tone and wooden timbre enclosure instruments ....would accept a Pre-Amp that returns the natural tone or relieve the digital tone. But there are " Pre Amp" and today's world know it as " tone re - Processors" 

I did a phase filter about 20 years ago using "all pass" filters, because all pass filters are for shifting phase.

They sometimes get used to shift phase by 90 degrees between two channels for low leakage hearing aid loops. Another novel feature is the true mono converter, which I believe was used by some AM mono broadcasters, which made the centre information 3dB less powerful, and sounded more "natural" than the commercial stations with their a+b/2.

Anyway, because of the large phase shifts of elliptical filters in early DACs and CD players, the highs would lag by upwards of 270 degrees or double that.

If the turnover frequency could be identified, then the all pass turnover could be tuned to the same frequency, and at some point would equate to 90 degrees, and if you add that to 270 degrees, you get 360 degrees (or 720 degrees), which is also zero degrees. Instead you get a time lag instead of a phase lag.

It seemed to "improve" the sound by reducing harshness, but with alterations to analogue filters, there was no mileage in it, so ended up down the memory hole.

My library of music is some 40  audio cassettes tapes, 100 Vinyl records and 200 Cd's and over byte full of 24 Bit download and apple music. 

The industry has established the " RIAA " equalisation for Vinyl replay in Pre-Amp and is well accepted and refined. CD''s was Philipps Data storage medium and tentatively to introduce in audio replay. It took over domestic home audio set up. But I kept my Record player and Cassette heads and successive generation of  new develop electronic Filters to the Digital to Analogue Conversion left me with a software or "app " to apply more analogue to the CD DAC output.

I could not do much to the Industry mandate CD' /DAC Red Book implications but I can to the AMP and it must be ANALOGUE and Transistor derived from Valve genetic. Now, if I can attenuate the CD output with a Transistor Pre amp ....the digital glare is dead and Music restore i n it's authenticity and creativity and emotionality. My Proprious and 70's design was not read in a glossy Invitation pamphlet to AUDIO Fair in London or Birmingham or Cologne but my distinct assessment of the components and design to hear Music.