It is already a proven fact, by JL Audio not me, that our head unit puts out a flat 2V signal that only needs converted to RCA connections. The HU does no processing at all and has no holes in the output. A cleansweep is completely useless. The stock HU does everything a normal person would need. If you are trying to win shows then that is a different story, but for 95% of humans you need nothing more than some good amps and good speakers to bring the system to life. It's amazing what you can find 2nd hand for dirt cheap, but still new in box. Amps are only as expensive as you are willing to pay. Many people are obsessed with the new and now, when you can pick up old school amps that still sound better than the new stuff. Processing is absolutely not needed at all in the Speed for anything less than a complete sound competition car. Do your research and pick the right pieces and it doesn't have to be expensive at all. I got really lucky and a lot of research netted me $150 worth of speakers that sounds fabulous in the car. I wanted specific amps, so I dropped $450 on two of the most sonically pure amps ever made. Worth every penny too and I wouldn't trade them for anything newer ever. $600 and the system was done basically. Subs are a different animal so price depends on what you want to do. It can still be done cheaply if you are a smart shopper. For most, the eD in the rear deck and a good Class D to drive it and you would be set for the life of the car. That only set me back about $150. Do I have another sub? Yes, but that was because the stock system had no bottom end at all and I did that back in the beginning trying to fix the Blows. I have about $300 in a shallow 12 and amp in the trunk, but that's over the top for a normal person. Did I buy a processor in the end? Yes, I bought a DQXS and DDC, but only because I like to press buttons and I couldn't pass a deal for the combo at $380 shipped. Did I need them? Not at all. The system sounded great without it and they are completely useless and confusing to a normal person. If I did it over, I could probably do it cheaper and still sound good. Not the same as mine, but quite good none the less. If I had more cash, it wouldn't sound much better without a lot of custom work like 3 ways in the front and things I wasn't in need of.
see Another audio thread. I personally found replacing just the amp and speakers to be worse than Bose. A processor or a nice HU is a must. 
