Yeah i am 55 Years old and could say i can heare stil around 17 kHz, its easey to test
take an Sinusgenarator on an Amp and move slowly from 10kHz to 20kHz and stop moving when you cant hear anything 
And Yes Harmonics are an big thing in listening Amps
also Noise to Signal Ratio and what kind of Cable you use from Amp to Speaker Combination
You could get higher or lower Highfrequencys with Different Cable because off Capacitance and different Basssound because of the inductance but on a passive Speaker with Crossover you has always an Big Coild in Front of an Bass Middriver so the Change is not that dramaticaly
But on aktiv Speaker its an different Story depending of how Long the Cable are i guess.
Not every Aktivspeaker need to have the Amp in the Wooden Speaker dEnclousure!
I dont realy like that at all, my Amps are all in an Aluminium Case on the Side off the Speakerenclousures! (care about Microphony effects, specialy on an Tube Amp i Bed)
And sure i never had the chance to listen an Tube Amp that costs more than 2000€ may be they
are better.
On the other Hand on what kind of Studio they do his recordings with Tube Amps?
May be only for Guitar Amp and may be on an Microphone Tube Amp
But thats an other Story to talk about ….LOL
The most studios have they Masters already digitaly saved so also using Analogue Recordings for an true full Analogue Chain isn’t easy to have anymore.
For Comparsion full digital with fully analogue Chains.
Best way, record an, let say acusticaly Guitar or Saxophone with an analogue Tapedeck and do youre Comparsions after copying the Track also to an CD or USB Stick in different Samplerates or so.
Or an big church organ, thats would be even better for deeper low end tones
For my personal taste, when i heared my first CD, around 1985 to 1990 not (sure enymore)
It was Vangelis China, i sold all my Analogue Records and Bought everything new on CD!!!
Even an cheep 500DM CD Player sounds much more Deep, Clean and Dynamic than any Record Player for 1000DM (DUAL or Thorens) @ this time, no cleaning needed @ al.
And for me i have never bought Audio Devices for more than 1500DM per piece, i was never rich
Normaly around 800 to 1000€ this days.
And now i like to build all i could by my self
Using Raspbarrypie 5 with Lyrion Music Server (Logitech Squeezeserver)
Building my own Speaker with efektive OEM Class D Amps and CamillaDSP for FIR Crossover two Audiointerfaces MOTU UL mk 5 with 16 Analogue Out Channels @all with 96kHz Samplefrequncy
waiting for an new MOTU release for an 24AO with that new MOTU 16A Design and latest DAC ships on it for 24 analogue Channels!!!
That would give me my Heaven and Flexibility for Speaker Settup on an full Surround aktiv Setup without using Souround AMP’s thats sounds ugly for my taste.
But thats me and my opinions for listening Music!
Every one has his own Audio Heaven and thats fine.
I own an Panasonic UDP9004 (payed 850€ when it was released) for Souround Movie and Music play
And befor i had different Cambridge Blueray Player around 1150€
So also have an old Onkyo TX-NR 5009 (new 3000€ @ release, got it for around 1500€ new some yeras later) Sorroundamp but thats sounds not good and i used only the AMP section for aktivate my Speaker @ that days 
Now it standing around without any use LOL
Before i had an Audio Analog Pre (Bellini) and stereo AMP (Corelli) with Passive Speakers (selfbuild with 2x AUDAX HM170Z0 and Focal inverse Kalotte Tweeter + Waveguide 2 / 1/2 Way Concept (50Liter Enclousures)) Was not that bad also.