Slaugh, I don't think that AVSTANG02 is trying to flame you. He has made some good points, just not in the most appropriate manor. Most of the members have all been in a situation close to yours. We spend the money on a product and find it very difficult to get the results we expect. It becomes increasingly difficult to ignore. I have spent months in my car so pissed off with the sound that I just turn off the radio. Being reminded of it everyday just compounds the tension. I strongly suggest that you turn off the HU and take a break from it for a week or two. It is amazing how a few days or hours away can help to clear your head. Once you have had some time away, start from scratch on your system. There are many issues that can be causing your troubles beyond the HU and gains.
First, buy a Digital Multi Meter. Don't go cheap with the Wal-Mart $15 dollar meter. You need one that is rated for around 30 to 40 amps on DC. It must also be sensitive enough on the AC range to detect a few volts. Some cheaper meters have a very limited range. Go to
http://www.sears.com and order one of there models. A decent meter will cost about 100 dollars for the amp rating. The cheaper one for about 30 will work but be carefull with your test tones. A 30Htz test tone will quickly make your amp pull its max current. If it exceeds 10amps (which that meter is rated for) you can damage it.
Once you have a meter, you want to check your cars voltage. Ensure that your altenator is putting out sufficiant voltage. Between your battery and altenator, you should read over 13 volts. A good altenator will be around 13.7 to 14 volts DC. If it is under 13 volts, you could have a voltage drop causing problems. Once the altenator is checked disconnect the battery. You will be checking the battery will all wires disconnected. It should read a strong 12. If it is under 12 volts DC, you need a new battery. Please make note that a failing altenator will almost always cause the battery to go bad.
Once you have checked the altenator and battery, double check your power and ground lines. Please post on here your power and ground line sizes and lengths. Please post both amps rms and max rating as well. You may be getting a drop in voltage due to small power lines or a poor connection. Look at your power line at the battery. Is there any lime built up on the connector. If so, clean it and reposition the connection. Ensure your ground line is good. Did you scrap away the paint around your grounding point? Is your grounding screw large enough? Most power issues are a result of poor grounding. I run all my grounds to a distribution block to ensure a large grounding surface. Now, take your multimeter and place it in ohms. The symbol that looks like a horse shoe. Place one end on your amp ground and the other on the grounding point. You are looking at the resistance in the line. The lower the number the better your ground. Leave one end on the ground post and place the other on various locations in the trunk. Do you see it drop in resistance. If so, your ground post may need to be cleaned or moved to a larger metal surface. I highly suggest you look at these areas. You entire system will be affected if the voltage is not correct to begin with.
You stated that a test tone moved your cone but music hardly makes it move. This has nothing to do with your preout capacity. A test tone requires more wattage than a music note due to it being constant. If your preout was weak it would still produce a weak test tone just as it did the music note. You should also take note that a test tone below 100 Htz should not be used for more than 30 seconds. Your amp can easily burn up if prolonged. As stated earlier, this could be more of a issue in the box volume or a crossover setting. To ensure that your crossover is not blocking some needed frequencies try a test tone at 40Htz. Test every 20 Htz up to 200. If your crossover is blocking some frequencies you will see it when the cone stops moving. Just let your amp cool down between tests. Due to crossover slopes, this won't be a perfect test but it may help to shed some light on the problem.
Prior to setting your gains, read all the tutorials you can. You will see that there are alot of assumptions that individuals make about gain settings. In reality, there is only one perfect setting. In order to achieve this setting, you need to understand what is happening at the HU and the amp. what AVSTANG02 was attempting to tell you, is that your HU voltage is not constant. If you are rated for 4 volts, it will reach the 4 volts at or just below clipping. Beyond this 4 volts, you may get some gain in voltage but most will be distortion. The same holds true with your amp. Your amp takes the voltage and ampifies while converting it to AC wattage. There is a max wattage that the amp can produce before it clipps. If your amps input is rated for .1 to 8 volts then it can produce that max wattage with .1 or up to 8 volts. Beyond 8 volts, it starts to limit the range you can increas your HU volume before it clips. The key is to match your HU voltage just under clipping with your amps input just below clipping. The only way these settings will be the same between two different people is if they both owned the same HU and amp. Even hardware that is rated the same may overexceed or underachieve what they claim.
The first step is to test your HU for clipping. I hit the reset button on my radio when I do this. You do not want any bass boost or eq on at this time. Do a search for tutorials on this. A scope is the best method but unpracticle for most people. Instead, search for a site that has a clipped and unclipped sine wave. Download each and listen to them very carefully. Place the unclipped sine wave on a cd and play it on your car. Only do one amp at a time. Place it at the lowest gain possible. You want your HU to clip before your amp in this test. Increase the HU volume until you hear the sine wave clip. Make note of this number and do not increase beyond it. In reality, you should stay five to ten numbers below. Any eq or bass boost will cause the HU to clip earlier. Some companies may clip at 80 percent of max while others may be set to stop before clipping. My current eclipse seems to increase to max without a clipped signal while my previous one clipped at about five numbers below. My previous Pioneer clipped at 15 below the max. It all varies. If you only have a sub amp in your car, place a normal speaker on the amp. It is very hard to hear a clipped signal from a sub.
Once your Hu is set, you need to do the amp gains. Since you are tuning the amp input to your HU's max output a weak preout will have no affect. Just be certain to have your sub volume at max prior to setting. There are plenty of tutorials on gain settings with a DMM, so I won't go into it. Good luck with your audio and just remember to take it easy.