Hi guys,
Ive decided to get the Alpine CDM-9823RR headunit, to replace my nick-knacked Concert in my 2000 W reg prefacelift A3 1.8T

please, visit here and tell me what you think:

Now, you now know my car spec, can I get one of these from the same place:
http://www.letsbuycaraudio.com/main/instAccess (click on Audi A3, no bose, pre2000)

"Installation Accessories - LBCA Leads PC9-401

Active System Adaptors allow you to change the original headunit and fit an aftermarket headunit to a car that already has an amplified (active) speaker system. This way you will maintain the vehicles existing amplifer and wiring to the speakers"

Do they just plug into existing blocks without rewiring, and Bob is my uncle?
AndyMac kindly offered some advice on this, but Ive got confused with 'Active Speaker Systems' and 'amps for rear speakers' and stuff. Hopefully you can diagnose what i need better now...