Custom wiring would be needed because the LX model is not wired for the external amp and speakers. The EX/SC stereo head unit does not have a built-in amp like the LX stereo, so you can't just drop it in the dash and expect it to work.to upgrade an LX to the EX radio you'll need more than just the headunit, you'll also need the amp (behind the passenger side front kick pannel) at a minimum and you should also hunt down the sub. Don't know about the wiring harness, that might be an issue too.
In the end, you'd be better served getting an aftermarket headunit that has the features you want and just install that instead.