1. You're system is not set up right
2. Gain is not volume control. Push it up beyond what the amp is capable of handling and you will damage either the amps, speakers or something else. Gain has to be set carefully. You need to take into account input voltage from the head unit, and tune the gain to a specific output voltage depending on where you want it. Not for n00bs.
3. audiotek is not known for making high quality amps. You're amp says 1000watts at 4ohms, 1500 watts at 2 ohms, 2000 watts at 1ohms. Being a maxxsonics product I can gaurantee that the amps are overrated. At the most id get your amp does 1300watts at 1ohms. Doubt its really clean at that power level.
4. You're maxing out your gains on your crossover, meaning you're driving it to clip. Most crossovers act as line drivers, meaning they increase the voltage going towards the amp. By doing this your trying to push too much power to the amp. So it's going into protect mode at low gain settings.
Unplug the amp. and measure the voltage going into the crossover. Write that number down (lets say its 3v)
Plug the crossover but not the amp back in and measure the voltage coming out of the crossover. Reduce the gain till it matches the figure you got before (In our case 3V)
Now reconnect your amp and set the gains properly using this tutorial
http://www.caraudio.com/forum/showthread.php?t=164826
The only reason you havent killed your L7's is because they can handle alot of power, the amp doesnt put out truly enough power for them, and the amp went into protect to prevent damage.
oh, and learn to spell
otherwise your subs will do this
but out the other end!!! 
Linear Mode
