Thanks, i7Baby, that's very helpful (sarcasm intended).
Early Sharp Aquos (and maybe later ones as well) often have sound issues. My current Sharp TV requires RCA cables to the soundbar in order to play some inputs, regardless of the source (Dish receiver, Roku, etc.). One input plays sound perfectly via TOSLINK, but only that one. I keep both TOSLINK and RCA cables hooked up so I can switch inputs and still have sound.
I've spent HOURS on the phone with Sharp--they don't even seem to understand the question. The latest firmware (2011?) didn't fix the problem. Recently I lost all sound and restored things to the status-quo via a "System Reset" in the Sharp menu.
did you ever get a solution to this? i have a similar situation with my LC-65LE643U. if i use the RCA audio outputs to drive my external amplifier, the sound works as intended for a while, but then will suddenly cut-out. the audio is is dead at both the RCA outputs, and the TV speakers are also dead. i had connected the cable box audio output to the amplifier, and the TV never failed (with no RCA audio output connections). unfortunately, this doesn't work for any other video input (internet, usb, dvd, etc).
under sharp warranty, i have had the main logic board replaced, however the problem still remains.
power down/up resolves the problem, as well as a full 'reset'. any of this sound familiar?