first, you need to get a box that will fit both subs and also fit in your trunk. then you need to get an amp that will properly power your subs. choice of amp is based on many different things, such as what kind of subs. in terms of wiring, depending on the subs and the power of the amp, you need to figure out what size power wire to run from your battery to the amp. a ground wire also needs to run from the amp to the chassis of the car. speaker wires will run from the amp to the subs. rca cables will run to the radio itself (usually...i have a zapco amp though which uses a balanced input from the rca's going into the amp). as for a new head unit...it depends on the car completely. some stock radios will support the subs and some wont. my infiniti g35 coupe and acura tl didnt require any new radios, and many newer cars wont. some will require a new radio, and most older cars will also. other than that...theres always a fuse running in the power wire. the size of the fuse depends on the amps power as well and the size of the power wire. theres also a fuse that goes in the amp. the amp should say on it what the maximum size fuse it can take is.
as you can see, a lot of these questions are easily answered with a little more information but unfortunately i dont have that. you can ask any shop that installs mobile audio equipment for advice as to wire size, amp choice, etc...seeing as it will make the most sense to go to one anyway in order to get all the equipment required in order to install it if you plan to do it on your own.
i hope i helped!!!
