i know that this is an old post but i thought i would answer your question so if you are still interested or anyone is interested then its answered.
the head unit will not have the same characteristics as the old stock one, they are made by different companies thus will do things differently like the antenna, there is no way around it without changing to a different head unit.
and the disk changer will never work again i am sorry
there are no more companies making disk changers thus no one is supporting them so if you have a disk changer the only way to get it to work is to get the head unit that worked with it from the factory, there is no after market head unit that works with disk changers. unless the new head unit has it built into the unit. if its in your trunk it wont work.