I got my HM-31 yesterday and have started to tinker with it. Initial results are favorable - problems that existed with my old MonoPrice switch look to be resolved. We'll be out of town this weekend, but I should have some detailed notes on the HM-31 online early next week. It does seem to be an easy way to expand the Model 990 to support video switching of up to four sources. It wouldn't work so well with the 970 because the DVI inputs aren't assignable, but I've got DVI2 assigned to three different sources (Video2, Video3, and Video5, if I remember correctly - they're labeled "CABLE", "OPPO981", and "HD-DVD") with each using a different digital audio input.