Well, I was just starting to get the FE-5680A board firmware functioning when the oscillator stopped working.
I don't know what the problem is, but about 10-20 seconds after you apply power, the output just stops. The lock LED never lights. I don't know if the unit just wore out (it had been powered up on my bench for a few months), or if something about the serial commands I sent was erroneous and bricked it.
I'm going to have to wait for another one to show up from eBay to continue, unless someone knows how to get this one working again.
The good news is that, so far as I can tell, the GPS board hardware does work properly.