SUCCESS!!
Well, sort of. I have the LE responding perfectly to a DIY DMX tester I built with a;
- Boarduino;
- the Tinkerit DmxSimple library;
- an RS485 chip, and;
- a bare-wire to RS485 patch cable.
The Arduino runs a simple 1-512 ramp cycle on channels 1-16.
So, the LE is working.
This, at least, isolates our problem to the ETD. (Good thing since this entire thread has been in the ETD sub-forum.

So;
FAIL...
Now that I've isolated the problem to the ETD, what board-level diagnostics may I perform? I don't have a scope or logic probe yet. (That's next on my list.)
Thanks to everyone who has helped thus far. Despite my frustration with the hardware, I've really enjoyed the support and graciousness of everyone here.
Michael