I noticed while flipping channels tonight that channel 575 (CSN+ HD) is now the Comcast Network HD, while 334 is the SD feed. Not that there is a whole lot to watch, but it's better than the floating Comcast Sportsnet logo when there are no live games. Nothing is in the program guide other than the the live games at this point.
I guess I spoke too soon. Now the channel is showing test patters and goofy clips of commercials along with still pictures of CSN commercials. For a little while, there was a lone camera angle of one person on a CSN Philly talk show with audio from only the left speaker.