When I first set up my 42LB6300, I ran coax straight in to the back. The live TV worked for me then. I now have it run through an STB, it's hit or miss with the Live TV button now. Sometimes it works, sometimes it takes me to the internal TV tuner and displays static. I think the WebOS on this TV is still a little under cooked. ARC keeps dropping off, The universal remote refuses to program for my Receiver, though the 47LA6900 programs fine with it.
This is my second 42LB6300. The first one, the wifi was inop, the HDMI board couldn't detect inputs, the TV tuner could not detect a signal. In fact the only thing that worked on it was the antenna and the audio continually dropped out. The WebOS continually crashed, even in the settings menu. It looked pretty though.