Fun fact, the O2 had an 'optional' expansion port that was an additional ~$1,000 or so... but the thing is, ALL the O2s had this port - it was that if you paid for it, they popped the plastic cover off the case to reveal the port...
The only blocking plates on the rear cover of an O2 usually cover the spot where the Flat Panel Adapter or Dual Monitor board goes, and it's not installed by default, or the spot where a PCI card would go, which, well, it's a PCI card.
The base model supported audio and "moose cam" (A webcam, in 1996!). If you paid extra you got video.
You could buy the base AV1 "analog" video I/O card and then plug an SDI expansion breakout board (I think the Miranda VIVO was the most popular) into the webcam port, instead of buying the much more expensive AV2 "digital" video I/O card.