How can I find out if my aftermarket amp can accept high level inputs?

The amp is on the right side (USA passenger side). The factory amp will have one input which is the fiber optic cable. Then it will have various outputs, which go to the speakers. Those outputs will carry "high level" or "speaker-level" amplified audio. Some aftermarket amps have speaker level-level inputs (such as these):

http://www.parts-express.com/cat/car...18;25418|25418

So, what you would do is splice the new amp in between the factory amp's speaker outputs and the speakers.

Do I will need an audio control?
Or I can just connect directly to the aftermarket amp?

Thanks for all your help Rudeney!!!

I believe you can connect directly and it will use the relative volume levels from the outputs of the factory amp. Basically, there are two "power levels" of audio output: pre-amp and amplified. Pre-amp levels are very low wattage, as in milliwatts, which not enough to power a speaker (though maybe enough to power small ear buds just to test the outputs). Pre-amp outputs still maintain volume control, but even at full blast, it's still a very low output. An amp just "steps-up" the wattage of the signal to higher wattage so it can move the speaker cones. Again, volume control is maintained by the amp relatively stepping up the pre-0map level to speaker levels. An aftermarket amp that has "speaker-level" inputs is designed to be connected to the high-level outputs of another amp. It then steps that down to pre-amp levels, then ramps it back up with its own amplifier circuits to speaker level.

I know this sounds kind of strange, to take a pre-amp signal and amplify it, just to drop it back down again, and then back up, but that's the least expensive way to make this work. For cars like yours (MY2005+) that use the MOST fiber optic system, you can buy an adapter that converts the fiber signals to pre-amp. This would basically mean you could totally remove the factory amp and use your own without all of this high/low/high conversion. Here's an example of such a converter:

http://www.autotoys.com/x/product.php?productid=16059

Rodney thank you very much for your very detail message it did teach me a lot and made me confident enough that I can do it instead of paying someone 900 dollars to do my system. I have done them on Japanese cars but I was scare to do it on this one. I will go with the hi/lo converter and splice it on the speaker wires.

Rodney one more question. If I put a hi/lo converter on the factory sub wires do I need another one for the inside speakers or one should be enough.

So you are going to use a generic high-level to low-level converter? If you are going to add amplification to more than just the sub, then you'll need more. Remember, the factory amp has 6 output channels: FL, FR, RL, RR, Center (on the dash) and Sub. Actually, it might have 8 - it might amp the sail panel tweeter individually, I can't remember. Anyhow, you'll need an amp channel for each speaker wire coming from the factory amp. My advice would be to use an aftermarket amp with built-in high-level inputs. The one I linked to at partsexpress.com has that. I don't know anything about that amp, but I do like Parts Express - good prices on decent gear.