Here is a link to the pac-swix on Crutchfiled that will allow you to continue to use your steering wheel controls. It can probably be found cheaper if you search around on the web.
http://www.crutchfield.com/S-3kVxFfm....asp?i=127SWIX
On a side note, If anyone reading this know's what all the steering whell controls contain and where they can be purchased seperately let me know. I have an SE that originally came with the single CD double din headunit and no steering wheel controls. I'd like to eventually add them (if it's possible) along with the pac-swix.