Hi VuDu
Welcome to the forum. You've got a couple of options. The A4 only has speaker connections for the front speakers at the HU. The rear speakers are driven by a puney little amp bolted to the nearside rear driver in the parcel shelf, from lineouts off the HU. As you are replacing the HU (good decision) you will need to run new speaker cable from your amp to the rears in order to by pass the Audi amp. You'll probably need to solder the new cable onto the speaker connections, see below. So the only pick up you need from your new setup is the front speaker loom. This is actually a standard ISO connector (a first for Audi to use industry standard connections) so all you need is an ISO male speaker adapter (about £8 from Halfords or Les Smith) which will give you 4 sets of speaker connections, with only the 2 middle ones working, for the front speakers. This will enable you to plug into the Audi harness and run new speaker cable back to the amp. The power for the HU is also standard ISO, so new HU should plug straight into the existing harness. Good Luck, you will notice a huge difference. I've replaced every component in my A4, mostly Alpine (4 x 50w amp, 1 x 300w amp & sub) Pioneer component speakers all round, Alpine HU & changer, and the results are superb.
