The main problem you have is you really need different equipment to do what you want to do. Ideally, this would mean a traditional AV receiver, or at least a more full fledged HTIB with proper digital inputs/outputs.
That said, there *may* be a workaround, depending on which audio outputs your HDTV has. Since the Panasonic only has a single R/L analog audio input, this means you need to employ some sort of A/B switch when you would like to toggle between analog audio from your Directv box, and Netflix audio from the HDTV back to your Panasonic DVD HT unit. The main wrench in this idea is that the LG LED HDTV only has digital optical output and no analog audio output. So a digital/analog converter w/ built in A/B switch (etc.) is what you are looking for. Radio Shack or perhaps Monoprice/Amazon might sell such a device, but you normally have to test them at home with your actual equipment to verify it will work properly. Your connections would be as follows:
Directv (HDMI out) --> (HDMI in) LG HDTV
Directv (analog audio out) --> (analog audio in) [A/B audio switch w/ digital-analog converter option]
[A/B audio switch] (analog audio out) --> (analog audio in) Panasonic HT
Panasonic HT (HDMI out) --> (HDMI in) LG HDTV
LG HDTV (digital optical out) --> (digital optical in) [A/B audio switch w/ digital/analog converter option]
*Keep in mind sometimes what Netflix sends out via the digital optical port is throttled. IOW, instead of DD5.1 surround, you only get 2.0 stereo. If there's a 'matrix surround' option (e.g. Dolby Pro Logic, etc.) on your Panasonic, that would be the setting to use to achieve a larger sound field/utilize all speakers.
Let us know how it goes.
I have a Panasonic DVD Home Theater System, model # SC-PT750, Directv reciever, and an LG55LS4500. I use HDMI from Directv to TV, obviously. And the standard red and white audio cable from sound system to Directv.
Here's my situation: For sound, I am not able to hook the TV directly to the sound system, a connection between the TV and the sound system doesn't work. However, I am able to get sound if I hook the sound system into the Directv reciever. So this is a good work around. But here's where this stinks, if I use my set top box to play movies from Netflix, I can't get the sound because the Directv reciever is no longer in the mix.
Does this sound familiar to anyone? Why can't the sound system go directly to the TV? And by the way, I have tried several TVs, none of them will work? Am I wiring something wrong? Is the sound system not capable of interacting with a new TV?