I normally use my macbook changing the channel from http://xfinitytv.comcast.net/tv-listings... However, on the bottom of this page, on the right corner should have DVR selection so you can switch which DVR you'd like to change the channel. I noticed that there's only one DVR selected, we used to have drop down button to select master bedroom or Family room DVRs.
It's been working for years, just noticed this issue about two weeks ago.
