I am gonna install a HU into my 330Ci... i went to Sounddomain and found the following items... the mounting bracket, car wiring harness and a antenna adaptor.. just wanna make sure these are the items i need to get in order to install a aftermarket deck... my friend got his HU installed at futureshop and when i asked him what else did he need for the install... he said he paid extra for bracket and some wirings... should i buy these 3 items online and bring it to a local shop or just get everything done at futureshop?