Three more photos from the OP...







The purple wire is the remote wire that tells the amplifier to turn on when the stereo is turned on. The wire it connects to in the third pictures should be a switched power source. The four wires shrouded in yellow carry the amplified signal from the amplifier back to factory harness location and connects back to the factory wires, which means it looks like the aftermarket components are essentially being driven through the factory wiring (as it is likely the same or smaller gauge of the two). You can (and should) verify the speakers are being driven by the amplifier and not the head unit by unplugging the RCA cables from the SNI-8 to see if the stereo is still audible. I know that sounds a bit paranoid, but I found a system being driven by the head unit alone on another member's stereo a while ago. It wasn't easy to identify because of some deceptive wiring hidden in the doors. All that being said, here is what to do next.

• Unplug the RCA cables from the SNI-8 and see if the stereo is still audible
  
  • If the stereo is not audible, then it's safe to assume the speakers are being driven by the amplifier. verify this by making sure the speakers are connected to the factory wires in the doors. the next step is to determine where the copper wires terminate
    
  • If the stereo is audible, then the speakears are actually being driven by the head unit (presumably through the copper wires). the next step is to determine if the amplifier is working properly and verify the use of the copper wires by tracing them through to the speakers in the doors.

 

OK with RCAs unplugged, door speakers do not work but tweeters work fine.

 

Now that I look at the amp again, the RCAs that are plugged into the SNI-8 arent even connected to the amp. The 'RCAs' connected to the amp have white and red heads with clearish tan wires unlike the Scosche brand (which is hooked to the SNI-8) which have blue heads and blue wires. Now where could the Scosche brand RCAs go? I understand the other 'RCAs' are spliced into the SNI-8/factory harness, but that still leaves us with two Scosche RCAs 'unconnected'...

 

OMG, that is so crazy! It sounds like the previous owner didn't want the tweeter stealing any power that could otherwise be used to drive the woofers. Interestingly, this makes it very easy to control +/- dB on the tweeters by adjusting the gain at the amplifier.

Since the KDC-X994 has line level outputs, you can/should get rid of the SNI-8. Once the SNI-8 is removed from the equation, conenct the Kenwood harness to the Honda adapter mentioned above, but connect the copper wires directly to the Kenwood harness. It will be a bit of a frankenstein setup if you don't want to redo the wiring in the doors. I'll try to put together a diagram later this evening.

 

You'll need to test with a multimeter to see if it's not just two sets of RCAs connected together to make the required length. They might even have used a 2 channel for one section and a 4 channel for the rest. At this point, I highly recommend pulling the wires or tracing them to see what you are dealing with. With this many unknowns, it's best not to make any assumptions.

 

Usually at this point id pack my stuff up and swing my car over to the audio place but since you guys are really trying to help me out i'll go ahead and complete the task. This week/weekend are really busy for me so i'll be in and out but we will get all this sorted out.

 

Here's a quick diagram to help sort things out. The layout to the left is the factory setup while the one on the right is what you're likely dealing with based on the info provided. The RCAs between the SNI-8 and amp are in two sections to indicate the possible extension. Of course, the only way to be sure about any of this is toe pull the door panels and follow the wires under the carpet.