Dude, the wiring that you have done sounds correct. However the problem with the amplifier going into clipping can have many sources of problems. Try some of this and it should run happy for years. Rockford amps are great, but as along time dealer we have done some serious work with them in order to solve problems. An amplifier will go into protection (red light) because something is telling it to, you need to find out what it is, maybe some of these steps will help you to find out.
(1) Resistance on a ground lead. What is this? This is the simplest way to explain it. Go into subway and eat a foot long sub and then have someone sow your crack shut. Current flows from negative to positive, your ground lead should in all cases be the same size as the power lead, by the sounds of your amp it should be a 4 gauge wire with a high strand count. Connect the ground lead direct to the battery. The assumed proper way of grounding is to keep the wire as short as possible, the problem here is that the resistance of the vehicle ground can be quite high. The correct way to ground your amp is to meter the ground resistance. If you take your meter and put one lead on the neg battery terminal and the other lead where you have your ground currently (assuming that it is grounded close to the amp) it will give you a measurement of resistance in ohms.(make sure the meter is set to measure resistance) Anything above .5 ohm means that you should be grounding to the battery. Make sure that you also upgrade the battery to vehicle ground as well.
(2) Make sure you have a cap for the amplifier.
(3) Turn your gain on your amp down, it is not a volume control, it is a matching device. Gains are designed to be turned down not up.
(4) Most cd and dvd players have what's called pre-outs, however even though some of them list 2/4/5 volt preouts, many of them do not actually give you this amount of voltage. Further to that the preouts actually clip -which causes distortion to be produced at the cd/dvd player that your amplifier says ok I'll amplify distorton for you, which causes the sub to produce the same distorion as well. You'll need som trial and error to find out where approximately your cd/dvd player starts to clip, turn your gain down on the amp when you find that level.
(5) Make sure the amp has adequate ventilation
(6) If the subs are new they may need to break in
(7) Loudness is also going to have alot to do with your box, post a reply to me about your box and vehicle and I'll go though it with you. I don't know if you have a local dealer there that is helping you, if you do great, if not I may not be local (Vancouver Island -BC) but when it's quiet here I don't mind helping others.
(8)For an experiment if you have a friend or dealer that carries Eclipse, try a Eclipse CD5423 cd player. It has a true 5volt non - clipping pre-out. You have a great system right now, just give it a try if you can, you just might be amazed. Eclipse is not a company that builds something to hit a price point, they build something to sound way better than anyone else. They have their strong points in the line and they have their weak points, trust me that the cd/dvd players are one of their strong ones. I'm not trying to sell you something, just give you some advice tht you may not have yet.
Top Secret, I can tell you but then my wife will kill me.