My plan:
I plan to keep the headunit (AM Radio!), but have the audio out of the headunit routed to the amps via the carputers line in.

When Linking the amps to the speakers, how would I go about doing this? getting a wiring harness, then taking the audio cables from the boot where the amps are to the dash?

In addition does anyone know if it is possible to have say dvd audio played through the analog audio out of the shuttle, but have the gps run through the optical out?

My Audio System will hopefully comprise of
4 Midranges + 1 Center + 2 Tweeters + 2 Subs
So I'm looking for a Dolby DTS DSP, 5 Channel Amp + 2 Crossovers for the tweeters, plus a 1 Channel amp capable of producing enough power for 2 subs. However, all I find 4 channel amps everywhere. Unless I get 4 Channel Amp for the 4 mid ranges and 2 tweeters and get a 2 channel amp, which can power the center speaker and subwoofers.

Lastly When hooking up the tweeters would I just connect them in parallel with the midrange with like a capacitor inbetween to act as the crossover?

And I'm guessing there is no dts software decoding, otherwise I could just use the onboard 5.1 ch sound outputs to interface with the amp without the need for the external dsp.