The NVIO chip could be doing quite a number of things. It looks to be handling HDCP for the dual link DVI connectors and SLI connectivity (the traces for the SLI connectors appear to run into this chip) besides RAMDAC functionality. The chip may have a digital audio pass through functionality for HDMI connectors. There is a spot at the end of the board where a 6 pin header can be soldered on, this could easy be for digital audio in for HDMI (or many other things). Replacing this chip alone could easily add video in/out and audio functionality to the card without having to redesign the entire GPU. There are two other digital display technologies on the horizon - Unified Display Interface and Display Port. Having an external chip control what connector is used allows for a bit of flexibility instead of wasting precious silicon space on the GPU itself to support all the various display technologies. By having an external chip for display out put should also for the main GPU to clock higher by not having to deal with as much noisy analog circuitry on chip. The downside to the NVIO is the additional cost of another chip and a more complex board layout. The GF 8800GTX board layout is insanely complex with a 384 bit wide memory bus anyway so that is pretty much a null point.