[Q] Take the ROM and kernel off a device topic

I have an HTC One x+ ATT (evitareul) and I am running an unnofficial version of CyanogenMod with too many bugs. I want to get the stock rom and kernel to restore to stock rom. Is there a way I can keep the /data part of the phone? I heard people saying you have to do a system wipe or some data will be left and the phone may not boot up? But my main question is: How would I get the stock rom and kernel off a device and put it into a format that can be flashed?