The initial test of modded Toshiba that I mentioned previously turned up a big problem: the stupid box stretches 4:3 DVDs {Update: this is fixed now, see below}. The result looks like this:

It is truly infuriating to realize that the firmware has all the information available to do the right thing. It knows the aspect ratio of the monitor (seen in the setup as 16:9). It knows the aspect ratio of the source. Oh yes, it does. If I hit the "Zoom" button on the remote, the played zooms, and when it zooms, it shows the correct ratio:

Here is the same pair of images for an anamorphic DVD:

There can be no reason to fail to add black bars at 100% zoom. It's a ridiculous bug. For the sake of Toshiba's reputation I hope it was added with the all-region mod.

I would've returned the player to the seller already, if only I knew of an alternative that actually worked.

UPDATE: I found the setting to fix the issue, by reading the manual very carefully. It turned out that access to the necessary settings is disabled if a disc is inserted... Good grief.