AFAIK, that's the limiting factor from being able to use only HDMI. How about the following scenario:

PS3-> HDMI -> DAV-IS50
Time Warner DVR -> Component -> DAV-IS50
Time Warner DVR -> digital optical -> DAV-IS50

DAV-IS50 -> HDMI -> TV

If that doesn't work in the sense that the Sony won't switch properly, I believe you could instead go directly from the DVR to the TV via Component.

There was a really helpful web site posted in the last month which gives you the opportunity to enter the various components and end up with steps needed to connect. Hopefully someone can provide that URL again. It can be hard to keep the models all straight(!)