Actually, I meant speaker housing adapters - to mount 'standard' 6.5" speaks into the 8" holes you get by removing the Bose woofers in the front door locations. It appears (to me) that Scosche is the only company still making / selling them now (-?) 'Making' is probably a misnomer...they're just selling excess inventory at this point, I'm sure.
I don't plan to replace any speakers. I just installed Bose woofers (purchased off eBay, w/enclosures) to replace the three-way speakers the PO had put in, and a pair of Alpine SPS-510 coaxials in the rear.
Much as I'd like to upgrade the HU--maybe get a sound quality bump, be able to play MP3s, maybe even get really ambitious and put in a back-up camera, it sounds like there's a distinct possibility of losing other things, incl. reliability.
Btw: I had the panel under the glove box off the other day. I was entertaining the idea of "restoring" my 2007's cabin air filter that GM removed. I don't think I'm going to be trying that, but, I did find there's a rectangular metal box and a bunch of wiring harness in there. Is that normal in a Bose system, or is it possibly something the PO left in there?
Nope. But, as I noted earlier (I think?): The PO had obviously upgraded the sound system at some point (there are marks on the back of the right rear seat where something had been mounted, the right rear speaker had been missing, the left rear speaker was a coaxial and the front door speakers were three-ways), then, I'm guessing, put the original Bose HU back in before trading it in.
So it's kind of looking like he left a harness behind, too. I wonder what it is? I didn't see any printing on the box that looked helpful. I'll have to open it up again and give it a re-look.
ETA: It's normal if you have XM Radio support, which my Trailblazer's Bose system does. It's the XM Radio module.
(Meanwhile: I'm wondering why my wife showed me an advert for a pimped-out 2014 Jeep Wrangler Freedom Edition...