Question for Amp Designers

I’m not an amp designer, but have built many tube and s/s for myself and friends.
There are too many parameters/factors to list that can do the above.
Just a couple for the
"laid back, mellow, & slower" can be.

limited bandwith
high impedance output (low damping factor)
little or no feedback, (creating the low damping factor)
Induced 2nd harmonic distortion
poor current ability
high impedance power supply (eg: tube reg)

and many more
Cheers George

Great question. I would like to know too.

Also lets not forget both amps are rated across the entire frequency spectrum, 20Hz-20kHz with the same THD at every frequency. So surely if the amp was tuned to sound better at certain frequencies, wouldn’t this affect the THD at these altered or accentuated frequencies to give the amp a signature sound? 

Good luck with that!!!!!

" What in the design gives these two amps the above sound signatures?"

Have you heard this for yourself or are you going by what someone else said?