Not sure about I30's. I'm sure you've done this, but I'll post it anyways. Go read up on Infiniti forums and see what they say about it. I am SURE there are people who have upgraded speakers or something else on an I30. If there are people that have put full systems into an ES300 - than I'm SURE someone's done an I30 and posted information online.
I would ONLY be concerned with 1 question:
1. Does your radio accept an AUX input via RCA?
a. If yes, you can hook up the carputer directly to the AUX in of your stock HU
b. If no, (which is prob. the answer) than you have to check with Blitzsafe or Soundgate and see if they make an AUX adapter unit for your car. Or search and see if someone has figured a mod for an AUX input