As the thread you linked suggests, the "Live TV" button on MCE remote control works. It takes you straight to the last played channel. MCCommand 30002 will do the same if you do not supply a channel number, or will go to specified channel if you do supply a channel number. Both of them work from anywhere, not just Theater View.
You can also customize Theater view and create a channels view in it. Then you can go to Theater view and start any channel from it.