The replacement DVI Detective box worked like a charm. I also had my new 6′ DVI-D cable in hand. I used the old box (custom EDID, bad signal connection) upstream of the replacement unit to program it and get the best of both worlds.
Also received my IRTrans (USB to IR transmit/receive device) and got it working with the iRed software on OS X. I used the ‘Tonto’ program from giantlaser to open someone else’s Presto CCF files, grab the codes from theirs, and use IRTrans to train my remote with them. Then I set those codes up in iRed as triggers, and used them to launch the python scripts to tell the TV to do stuff. (Via AppleScript.)
I know it sounds kind of Rube Goldbergian, but it actually works a lot more reliably than trying to program macros in my universal remote.
All this, just to overcome two fundamental shortcomings of this LCD TV: Lack of native resolution in the EDID, and lack of discrete IR codes to switch between inputs.
Now that it’s done I’m quite relieved!