SQ impact from a tube preamp after signal leaving an AVR?

No we don’t.  We buy $500 avr’s and sit insonic bliss 🤦🏻‍♂️

So the merits of higher priced tube preamps may be in doubt.  The absurdity of buying overpriced components.  Yet we do it.  

This horse has been bludgeoned to death already by the OP who seems obsessed with asking the same question from as many redundant angles as he’ll continue to get answers for.  Enjoy the insanity people.  Peace out. 

Funny, good analogy and pivot.  And, no use of sunglasses or equalizers in the house here. Later learned how much more we could see and hear without them.

Oh the memories. Messed with a number of ADC, SoundCraftsman, Sansui crossovers in the 70s and 80s though. Kinda like this one.
https://i.etsystatic.com/15730567/r/il/8d1564/1542010526/il_1588xN.1542010526_7smm.jpg

Must say though, if I needed or wanted an equalizer today, this little Schiit Loki is pretty cool for $149
https://www.schiit.com/public/upload/general/loki-mini-front-1920.jpg

You can't add information, but that does not mean you won't prefer the sound after adding a tube-pre.  I wonder if other responders have ever worn sunglasses or used an equalizer and liked the results?

emergingsoul, the AVR itself is the signal quality impact.

Ditto what millercarbon said, re-read his last two sentences again, "G-D" right.

You’re making some fundamentally flawed assumptions here. Its not just avrs and pre amps. The signal flowing through everything is additionally impacted when flowing through everything else. No, home theater sound does not improve after additional processing... from anything.

This is a fundamental misunderstanding you are making, but it is a very common one a lot of people make. Nothing, no component, no wire, no tube, no circuit of any kind, can ever make anything better. The very best anything can do is to not harm the signal, to pass it unmolested.

Think of a window. Imagine your stereo or home theater as a window on the performance. How can a window make it any better? It can’t. The glass can be clean or dirty, colored or clear, flat or curved and distorted. The very best it can possibly be is an open frame with no glass no nothing just air. Its impossible for the window to improve anything, because the minute it does that its no longer a window. Its a microscope, or a telescope, or anything other than a window.

Got it? So the avr does way more harm or damage, the tube pre amp does way less, but never at any point does anything ever get any better. That’s why its so important to get the G-D avr out of the room. The massive harm it does can never be made right.