I'm new to this site. I have owned a black 2006 4.8is just over a year and I love it! The stereo is lacking though. After about a year of researching dead ends I finally got it figured out. The plan is to keep the stock navigation deck and everything else except the stock speakers. I was told that you can install a digital signal processor (DSP) Directly to the outgoing speaker wires from the stock dsp amp. The added dsp will basically translate the signal to analog so you can just add an amp and speakers. Then I found jl audio makes a dsp 5 channel amp. Jl audio VX700/5i. They make more powerful ones, but this one is perfect for my build. One channel per door and one for the sub. I already got the speakers, (jl audio c2-600 components.) And getting the JL audio 10"w1 stealth box next week. Once I have everything in hand I will take pictures of the install. I hope some of this info will be of help to someone, it took me a year to get enough info to be confident in this build.