Using a VGA adapter will work only if the display supports DVI-I input. DVI was developed as an interface for LCD computer monitors (which are digital display devices) and as such was a digital interface, but the developers were unwilling to abandon trusty analog video and allowed for three forms of DVI: DVI-D (digital only, single link or double link), DVI-A (analog only, for the familiar old analog video signals), and DVI-I (a connector that carries both digital and analog, so the device can input - or output, if it's a video card - either analog or digital based on your need).

Most of today's HDTV's either have HDMI (which borrows DVI's digital video side but left the analog video behind) or DVI-D. There are a few devices around that offer DVI-I (mostly front projectors, since many trace their lineage back to the business projector market). Only a DVI-I device will be able to work with DVI-VGA adapters, and then only if those four pins are in place throughout the entire signal path. According to Projector Central , the Optima H31's DVI input is a DVI-I input, so it would work with a VGA adapter, but if you can't plug a DVI-I cable into the 990's DVI ports without removing those four pins then you wouldn't be able to use the 990's switching with a VGA adapter in there somewhere.

Only loosely related question... When is Microsoft going to go ahead and find a way to put HDMI into the 360? For that matter (and get even more loosely related), I wonder if an inexpensive component to VGA adapter and a VGA to DVI adapter would be used to let you use that DVI-I cable to your Optima with all of your analog sources? (Component monitor output from 990 to the converter, converter VGA output to the VGA/DVI adapter, DVI-I cable from there to the projector...) It's late and my mind is wandering in potentially crazy directions.