07 Yukon Denali Bose system w/nav upgrade?

I am looking to upgrade the factory Bose system but keep the factory nav unit. I would consider either just replacing the speakers with better ones or upgrading the amps and speakers and adding a sub. From what I have read the factory amp controls a lot of the features of the factory system so it may just be easier to just upgrade the speakers but I would still really like to add a sub and amp if possible.

You can easily add an amplifier and subs. You can easily Add an amplifier for your door speakers.    You do have to leave the Bose amplifier. You should use the rear outputs to feed both the front and rear inputs of your new amplifier. The reason for this is the door dinger will run you out of the vehicle. If you use the OnStar or factory bluetooth or want to keep your door dinger, you will need to install a speaker under or behind the dash to use these.

Do I tap into the rear outputs from the head unit or off of the Bose amp? Is a line level adapter needed? I have amps from a system I used back in the day (Phoenix Gold titanium series, 500.4 for the doors and 2 600.2 for the subs). I have not found a ton of info on on what I am looking to do. Can I use the center channel speaker for the chime, on star and nav? Or should I keep the center channel powered off of the Bose amp?

Catch the output of the amplifier. If there is enough vocal info coming from the center speaker that will be fine. Pac-Audio.com 's SNI-35 would be a good choice for the line input converter.