I am hoping to purchase a 2007 A3 but would want to replace the head unit with one that has a better interface for an IPOD. There appear to be a lot of good head units out there (Alpine, Pioneer, etc.) but how feasible and cost-effective is it to have someone install one of these? Is it true that the whole car needs to be rewired? Are there options that will allow the steering wheel controls to still work? Thanks.