Many CD players which I "lampized" (close to 100)  has the original circuit intact. I install new RCA or XLR sockets so direct comparison is possible anytime because the old outputs are still existing and active. And should you desire to stick to the original sound for whatever reason, you have it. (not true for Iout types of DAC like 1541A which must be cut off from the old circuit).
First impression is that the sound is louder. It is really louder because I do not restrict the natural amplification of lampizator by means of any resistors. The amplification is by the factor of 9x (for 6H6P) and of 20x (for 6H1P) The output of tube is directly connected to the amplifier.  (well, via a capacitor). Most amplifiers enjoy the easy drive of high signal and respond with better sound.
The second most apparent feature is that the sound stage is twice as high as before and twice as deep. It is also so wide it goes WAY BEYOND the speakers in width.
Details are unleashed in unbelievable manner. You hear so many things never heard before that it sounds like a new recording. Details are not artificial kind , "created"  by means of shifted high frequencies - they are natural.
Sound is much more dynamic. It has powerful but natural bass,  lots of rhythmic drive. It envelopes you in realistic and hallucinogenic sound field. You can hear individual musicians separately (what each one is doing) and at the same time you enjoy the musical event as a whole, not a bunch of separate musicians. You can follow each player if you wish to follow him, but never get disconnected from the event's atmosphere as a whole.
You don't get tired of listening, it is so smooth and liquid, in contrary - you want more and more.
The music sounds good on all volume levels, even very low, but the clean and natural sound enables you to play much louder than before without fatigue. Your ears are so happy that they ask for MORE.
Returning to original output signal sounds ... funny. Most listener react with laughter. This is their disbelief that such transformation is possible.
The best news is that great recordings sound fantastic, but also recordings previously considered bad - harsh, or flat or old fashioned - now sound great and very interesting.
Best experience is to try live recordings - the natural sound of these un-manipulated tracks really shines.

There is no mythology, no tricks or voo doo in this superiority. There is nothing about tubes that makes them so special. It is the simplicity of circuits, careful execution, lack of feedback and high available energy storage in power supplies  (proportional to U squared !!!)

Having said all that - the full potential of lampizator-tweaked CDP's can only be realized on tube amplifiers and adequate (sensitive and natural sounding) speakers.

I would go as far as saying that removal of the last remaining half of op-amp improves things equally dramatically as the lampizator itself.

And the last point: some people claim, that tubes are sounding interesting because they add "pleasant harmonic distortions" to the sound, they colour it, they rosy eyeglass the music.

THERE IS NOTHING MORE WRONG.
This statement means that the person who says it is either deaf, or he is a transistor salesman, or that he never heard a proper tubed kit.
I challenge anybody who claims this heresy to be truth and putting down tubes to meet me at dusk by the river and fight with naked fists.