Im thinking of getting the RNS-E for my A3 TDI 2004 as my screen as gone on the BOSE Audi Symphony. 1) Where is the cheapest to buy a unit and what is needed to fit? Link would be great, ebay or private sale. 2) Will it fit straight in after taking the old unit out? 3) Would I need extra leads etc & housing? I have a Parott Bluetooth, Bose & 6 CD in glove box & the Audi symphony is a 6 CD too. 4) Will the Sound quality change with the BOSE linked to the RNS-E? Get better?