* I am just joining here with 1 month experience in a ZL1 vert - so hopefully the audio experts can say definitively - but the change in "tone" you notice top up/top down is probably some sort of "noise cancellation" being added when the vert top is down.
* Note: many of the stereo upgrades talk about "clipping the ANC (automatic noise cancellation) mics in the doors". I think I might know where these are - they might be little things that look like tiny defogger vents at the back of the door. There's a pic below with the door off.
https://www.camaro6.com/forums/showthread.php?t=499824
https://www.camaro6.com/forums/showthread.php?t=505338
* This is probably not the answer you want, but I think the Bose sound is not good in any top up/top down configuration, so I encourage you to investigate a stereo upgrade.
* Here's some links for you, and I am in the middle of my upgrade with the car at the shop and about 50% done.
https://www.camaro6.com/forums/showt...ght=drfeelgood
https://www.camaro6.com/forums/showt...stereo+upgrade
https://www.camaro6.com/forums/showthread.php?t=497975
https://www.camaro6.com/forums/showthread.php?t=503822
https://www.camaro6.com/forums/showthread.php?t=561714