That would be the answer to my question, which was badly put. Looked, but didn't see a picture or diagram of the PCB with the physical location of the connector types labeled last night. I was the one who suggested the Extron Scaler.
TTL would need to be converted to an analog signal, no? Guessing here, but a digital feed to the analog scaler might explain those crazy lined patterns showing up at crazy settings you needed to get them to display through the Extron?
Not awake, but a quick peek seems to point to ECL being an analog circuit/interface? From the little I had time to read, it seems strange to be used for video? Might it have made for inexpensive boards on the monitor side of things?
WAG would be that, if analog, it'll be a simple thing to use the ECL interface? TTL digital signal can be converted to analog, but seems like an unnecessary extra step if a clean analog feed is available. Low signal to noise ration of an ECL circuit should be better in every way but power consumption from my quick read.
Gotta get ready for work . . .
edit: if that's not ECL, I'd bet it's a proprietary analog output as were some of the several graphic card interfaces on DE-9 for early compacts IIRC.