...while BOSE would tell you not to set any Bass or Treble at all, other than stock. They often try to convince the car manufacturers to remove the controls with a BOSE system fitted as their settings are as they should, but "the buyers" (you) wouldn't accept that, so most of the time the stereo/car keeps the Bass & Treble settings.
What they are more successful at is having the separate EQ removed.*
The BOSE system is much more than new speakers. It's a separate pre-def EQ for the car (specifically tuned by BOSE), band filters, and new amp, and a woofer. Many times it also adds speakers.
Point made: With any "hi def" stereo, don't touch the Bass/Treble (unless maybe if your recording is really crap)
I've had BOSE in my 4 last cars (156, 156, Saab 9-3 and G QV) and I'm very pleased.