First of all, your 6x9s are crackling because the subs are drawing too much power, YOU NEED AN AMPLIFIER. The amplified outputs from your radio to your 6x9s are probably about 50-150w and the draw on those subs is probably 150w ea. Therefore, every time they hit, they suck up all the power for your 6x9s and you're left with a 'crackle'.
Also, those Sony Xplod subs say 1100 MAX but that 1100 watts is the absolute maximum power they were able to produce with those subs at the factory. Look at the box or online and find the RMS rating for those subs, that's the REAL power it typically draws. As I said before it's most likely around 150 watts per sub. What you're going to want to do is purchase an amp (sony would be fine) that puts out the same wattage (RMS) as the RMS on your subs. For example, if the subs are 150w RMS, you're going to want an amp that puts out 300w RMS. You DO NOT want to under power your subs, as this is the #1 reason people break their speakers.
Hope that helps.
-Mike