I just added the 500watt mono S.O Amp they had there at Crutchfield and it had a cable remote control. $100. I spliced in at the Sony amp for turn on in the left side of the trunk. I used the Audio Control LC2I $60 and use the High level inputs off the 6x9 deck speakers to run that. Soldered it to the speaker leads there right at the speaker under the deck. I could have used the High level inputs that the Amp had but wanted some more options with the Audi Control unit.
It is awesome for the Money I spent. Totally worth it. $190 for subs. $100 for the amp. $60 for the processor. It slams now. The limit is the Sony Amp and factory speakers. I dont know how the bass is getting into the passenger compartment but it does. I thought I might have to crack the rear seats or remove the factory 6x9 subs.