I want to get and amp and subwoofer for my X. Do i need a new stereo to wire that into?

No.

Are there already connections to use to hood up and amp to the radio?

No.

Could someone explain this? How would he hook up an amp w/out preouts on the head unit... are there any on the stock head unit? I am wondering the same thing so if someone could help, that would be great. I bought my X used and there is an amp attached to the backseat but not hooked up to the stereo. I'm thinking the person had some aftermarket stereo and just took it out when they sold it but I would love to be able to just wire it in. thanks.

Simple answer, High low adapter, go to RS, BB, or any other car stereo joint and ask for one, cheers.

Straight and to the point. Thank you, I'll head over there today on lunch.

A lot of amps also offer speaker level input.
All you need to do is run a speaker lead into the amp. FOr a remote wire just use any of the 12 volt power sources that go on and off with the vehicle(so the amp doesnt stay on all the time)

Get a RCA line converter. The easy way: Connect the left and right rear speaker wires to the rca converter $20. Then run a remote led toggle switch from under the hood $4.99 to $9.99. I could not find the remote on the Xterra radio, w/ 6 disc. Plug in the rca's and also run your power to the battery with a fuse. All you have to remember is to turn the toggle switch off because its manual turn off. I have not had any troubles with it so far. Just connect a bright toggle so you remember to turn the amp off.