Thanks very much for your responses, Bruce and Crash!
That's an excellent suggestion, Crash! Makes a lot of sense to me.
It's also entirely possible, that warming up the desk for a while got the DIO.8 card recognized, and not messing with the word clock setup, since I had the desk running for about an hour or so, before restarting, to see if the word clock input was recognized now (...and that's where the DIO.8 in the Tape 1-8 slot came back as well).
I left it running all evening yesterday, and booted for the first time today. It's still recognized. Now I have word clock issues again, and had to start up 4 times already, troubleshooting it, but the DIO.8 that caused problems before was now found every time. Could also be, because it's a pretty warm day here in LA today (95 Fahrenheit).
I'll definitely keep the "warm up" tip in mind, if one of the cards isn't found again in the future. THANK YOU!!!
Now on to troubleshooting the word clock issue again. Always something else with this thing. I hope I'll get it stable some day soon.
Thanks again!