Depends;

What you could do is run a good amp to your interiors make sure the amp has a pre out built in which most high end amps do. This will sastisfy you for the time being. If later you want to listen to a wide range of music you can get a sub and amp and just piggy back of the interior amp. Watch how much power your sending to those 4 ways though with out a cross over if ya over power them you'll blow em.