The XBR6 will show a status menu for TVGOS, not a black/blank screen, while waiting for its initial download.
I, too, have occasional weird problems with my XBR6's TVGOS. The only "fix" I have ever found, is to do a full factory reset of the TV in general. Then setup everything again, including setting up TVGOS again. Yea, getting all the settings back to what you had them, is frustrating.
IMHO, Sony needs to fix this in a firmware update. However, I am sure that the XBR6 is too old for Sony to bother.