Hi Rich,
The black QT method will work with the Io LA.
First, try connecting a consumer TV directly to the Io LA via composite instead of through the Beta deck to simplify things (you might have line blanking enabled on the deck). Make sure CC1 is enabled on the TV.
Also make sure your FCP sequence and output settings are set to 720x486 (not 720x480).
If you still aren't seeing the captions, have the CC service company do a calibration test for your system to make sure their settings are right, and then they can send you a new black QT CC file with the correct settings.
Hope this helps,
Jason Livingston
CPC Closed Captioning