I've been meaning to post this but wanted to finish up getting it working first. Here's my findings so far. I'm not sure if this will help the LC guys, but worth reading and maybe trying the headunit-to-amp ground strap described:
Vehicle is a 2007 LX470
Scenario 1: Teyes with Factory Amp and speakers using G-socket speaker outputs:
Exactly as described above. Everything works great. The amp gain is controlled by the volume knob. The headunit volume is controlled with the headunit or steering wheel controls. The headunit emits a very slight hiss, but you can't even hear it until the volume knob is 80%+. The solution is to keep the volume knob around 70% and use the headunit to control the volume. Set the headunit sound conditioning to about 10% for best results. Note that some LXs will require the harness re-wire for rear speakers to work properly.
Scenario 2: Teyes with aftermarket Amp and Speakers:
I tried a couple of different configurations here:
RCA outs
Initial Result
Terrible ground noise. Whine with the ignition on and rpm-dependent alternator whine with the truck running. The gain on the aftermarket amp has to be set to almost zero to avoid the humming.
Diagnostic steps I've tried and their results:
1) Hook up an MP3 player to the amp to eliminate the amp as the problem. This results in crystal clear sound with no whine.
2) Hook the headunit up to a 120v AC amp and a set of headphones using the RCA outs to eliminate the headunit as the problem. The result is AGAIN crystal clear sound with no whine.
So the amp works by itself and the headunit works by itself. The problem is the combination of the two.
Ground solution
This is usually a ground level difference between the two components that results in voltage travelling across whatever path connects the two components, which in our case are the RCA cables, and hence the noise. The solution is typically to provide an even better path for the voltage difference so I ran an 8 gauge cable from the Headunit ground (G Socket) to the Amp ground. The whine went WAY down to maybe 30% of what it was before, but it's still loud enough to be annoying with the amp gain at only 30%.
I also ran both the Amp and headunit grounds directly to the battery with no additional difference.
I also grounded the sleeve of the RCA cables with no difference.
12V Noise Filter solution
First I pulled 12V from the Amp's noise filter 12v line. This meant that both the power and ground were shared between the amp and the headunit. The whine didn't decrease anymore than just the shared ground.
Then I ordered 3 12v noise filters from Amazon. The first one arrived same-day and I installed it. No difference. The other two arrived today, but I'm traveling so won't be able to try them for a few days. Will report back.
Speaker Outs
I wired an RCA cable to the end of the G-Socket speaker wires (+ and -). Made no difference.
Optical Outs
I ran an optical to RCA DAC (takes optical cable in and splits into 6 RCAs). That's an AC-powered box so I ran it from my shore power. It worked perfectly. It totally eliminated the whine. I haven't been able to find a 12v version and I'm afraid that even if I did, it would cause the same problem with a power/ground delta between the DAC and the Amp. This is on my list to try, though.
Current Situation
Right now I have the headunit and amp grounds wired togehter and the amp gain set to just below where the whine bothers me with the music off. That's about 30% gain. It's not terrible, but my kids, who have better hearing than me, get driven crazy by the whine. I hooked the amp remote up to the amp wire on the back of the teyes (A socket I think?) and can now turn the amp on and off from the headunit. When I want it REALLY silent, I can go to settings->device->sound->Amp and turn the amp remote off.
List of things to try
I'm not giving up. I want to get this thing working. Here's what's next:
1) Install an amp (or DSP) with an optical in to electrically isolate the headunit from the amp
2) Install the other two noise filters to see if they work better
3) Install chokes on the 12v power line coming into the headunit
4) Install a ground loop isolator on the RCAs, but I really feel like this is a hack and I don't love the idea
5) Do the "big three" upgrade by beefing up the battery-to-chasis strap, engine-to-chasis strap, and alternator-to-battery upgrade wiring
6) Put a Newmar 150 amp noise filter on the alternator to stop the noise at its source
Still a work in progress, but at least it's progress