Lots of fiddling, finally got connection with openOCD...

Who knows whether it'd've worked without some of the additional-fiddling (e.g. figuring out where /MCLR should connect, etc.) but it does work now. THE BIG "DUH" was I was *certain* I breadboarded the MX2xx series chip, but apparently had breadboarded the MX1xx series chip, instead. (They've *very slightly* different pinouts). Swapped it out, and it connects.

I'll update the "details" section with better pinout info, and whatnot.

Yesterday's unposted post:

Not sure what's wrong with my setup, but it's not detecting my chip yet...

Had to reinstall openocd, as apparently the last time I used it was on a different (and now defunct) computer. So, thought maybe something was wrong with the setup, but apparently I'm using the exact same version (actually, installed from the same .deb)... And did some searching 'round the web and found that others have had [some amount of] success with even older versions.

A couple useful resources:

This page suggests it's possible, and with my version, and using a configuration-file that exists... (Rather'n having to configure each setting manually)
https://forum.sparkfun.com/viewtopic.php?f=18&t=28623

This page suggests TRST should be connected to pin1 /MCLR
https://github.com/kinsamanka/PICnc-V2/wiki/OpenOCD-PIC32-Programmer

Tried TRST on MCLR, both directly-connected and through a transistor-inverter... Still nogo.

Finally, decided to hook up the ol' Cable Box again, just to make sure the danged FT2232 board still works... It didn't, at first, but then I connected nTRST to VREF and it did. So.... Something to think about, in here... I don't know what, exactly.