Ok, car is now fixed! I'm summarizing everything I've learned over this whole ordeal here for future reference (it wouldn't let me do it in the first post, oh well). I wasn't able to find much on failed radio units, so I hope this helps someone in the future...
If your radio head unit dies (which presented in my car by the infotainment display being completely blank), you're looking at minimum $1200 for a new part (non Nav version). Ridiculous, right? So go to ebay, you can usually find several used ones in the $100 range, some gen1 model years were common with Malibus as well and will work. You need to be sure of the
exact part number, though. Either pull your dead one or talk to the dealer Parts Dept to get the one that goes in according to your VIN. Now here's where it gets fun... a used part has a VIN stored in it, and it won't match your car's VIN. So when you install it, it will just display the word "Locked" on the screen and not allow you to do anything. No biggie, go to the dealer, they'll program that Malibu one to Volt software but
may not be able to remove the VIN lock. They said they should be able to, but I've found several people who also had a dealer that was unable to unlock it. This seems to be more and more common for some reason, so I would assume they will be unable to unlock it. Now what? There are some 3rd party specialty shops that can "hack" the unlock (
www.whiteautoandmedia.com is well known on this forum, I found another one but can't recall the name). My dealer went the extra mile and worked with one of his distributors who was able to do it "officially". So I had to remove the box again, take it to the dealer, and they shipped it to their distributor. It will come back with a blank VIN, and of course the car isn't smart enough to deal with that, so you'll have to reinstall the box and have the dealer program your VIN in. This whole process took about 4 weeks and a lot of hassle, but I saved a lot over just buying the new part. Though it was still annoyingly expensive for a friggin' radio, and my car had reduced functionality during those weeks (no display means no audio, no charge settings, no real HVAC control, etc).
Dealer diagnose dead radio $160 (I couldn't diagnose on my own, as it could have been many things)
Used radio on ebay (Malibu) $42
Dealer program / fail unlock $120
Distributor unlock $150
Dealer install, VIN learn $120 (a nicer dealer would have done this for free, since they failed earlier)
Total cost after fees $611
On a just-over-3-year-old Volt (so just out of warranty), this was an annoying failure. Made much more annoying by the theft-prevention VIN locking on a box that NO ONE WOULD STEAL. If I had to do it over again, once I knew it was the radio, I would have taken my ebay radio and sent it to one of the 3rd party places, I
think they can hack it such that you don't need the dealer to do the VIN learn, the box will just accept the new VIN the first time it's used in your car. They charge $100-200 for this, so that may have saved me a few hundred dollars. Or a nicer dealer would have charged less for programming / VIN learn... it only takes a few minutes (I like my place, but I think they didn't like that I didn't buy their $1200 box). Hope this info helps someone else.